Advice, thoughts?

Yeah, true. She's acting like her getting on new meds and going to counseling and staying is her trying. There has to be progress if this is true. If I don't see any progress, I gotta be done with this shit. I'm gonna explode if I don't.

It also sounds like you have been enabling her destructive behavior. Letting her string you along will only reinforce it.

sdiamond, please read what I'm going to say to you very carefully. You don't have time to go through the normal process of defogging in this scenario without a very expensive consequence.

You story maps VERY closely to mine.
Depression - check
Celibacy - increasingly, since the wedding day - check
Her affair - check
You trying various methods of enticement and her then passing your persistence and her captiluation as your abuse of her - check
Her wanting to keep the marriage going - check
Gaslighting you by dangling further corrective measures that take a long time and that might or might not end up helping - check

She's been this way since the beginning of the marriage - or at least she has felt this way.
Trapped.
Whether she's into you or not, she views the marriage itself AS the trap. I'd warrant the sex fell off in stages, increasing with each level of marital investment. Start with the wedding day, then honeymoon, then house, then kids - right?
She's jujitsued your willingness to work on this with her and made it into PTSD. She takes no responsibility for letting it get this bad. Whether it is BPD or Depression, they cannot be cured, and if they are, they do not cause sexual desire for a person they actively don't want. She HAS a libido. She's acting out her resentment of you for marrying her.

She's been this way for 25 years. Longer even - she didn't want to get married and viewed it as her mistake - but blames you.
Correct the mistake.

File ASAP. File immediately - as fast as you can. Pay extra to do it. Do everything you can to get in under the wire.
If, as I suspect, you are still tied to working on the marriage, and it works out in the long run, then you can agree to take those measures to create a new relationship AFTER you have filed. But doing it the way you are thinking about it CLEARLY puts ALL the financial risk and responsibility on you, and the permanent financial liability will lessen your viability with subsequent partners (which is a lot to think about now, but won't be in time).

Mental illness, including BPD and depression, or Borderline, are not easy fixes. The meds, if they can be taken, are not an exact science and take a long time to get right, if they ever get right. Therapy, even years of it - as we did - can help your communication and relationship overall, but it is still a NORMAL outcome to not restore or create a sexual connection (despite your interpersonal skills improving). It won't ever work when one or both partners doesn't WANT to make it work, and your wife wants the marriage to work (or to have the benefits of a marriage that suit her) without the desire. She BLAMES you, and will use the therapy as a place to externalize and validate that blame.

If she's serious about it working, then she can shoulder her part of this burden - it's the least she can do as the one who has left the relationship. File for divorce before the week ends. Tell her if you need to, beforehand. Cover your ass - you have such a low % of success. But if she wants to work on it together, then she can do that after divorce is filed. Your family counselor can then pursue what's called a "therapeutic separation", as opposed to a separation intending to lead to a divorce.

If you are worried that she will react poorly to the loss of permanent alimony, then you really do have a line onto the level she's operating at consistent with taking your money and paying her masseuss. She already blames you for "giving her PTSD" - so she's justified in her mind and has a lot to gain by stretching this out a bit longer.

The money is not going to, one way or another, create desire for you.

Are you sure it goes from the date of license and not the date of the wedding? I imagine people could get a license and yet not marry (what happens if you call the wedding off?). It's worth getting the legal advice. You'd willingly pay more for insurance to protect less income than what you are staring at now with the legal fee and burning a vacation day.

I know it feels to you like the two of you are just starting to deal with this problem. I can tell you from thousands of stories on here that - 25 years in, you are well at the end of the problem - Stage 4 cancer.

The 6 months thing isn't a practical solution. Couples therapy will likely go longer.
The idea of "nothing changes" isn't a great goal to set. Things will likely change. You will fight more. You might likely improve your communication and articulate yourselves, but you won't have desire in your life.

In my situation, I went to counselling for years. I learned and proposed just about every unspeakable but legal kink and style I could reasonably think of, in case it was that. Eventually opened the relationship a crack on both sides, and after a couple years of her cruel failures at that and further therapy after we closed it again, I asked for a separation.  I was with her 18 years, married 13. 2 kids.

Yes, prior to opening the relationship but after years of near celibacy and sexual dysfunction and resentment, she did have an affair.

When we separated, she left the house to move into an apartment up the street. We still have merged finances to save money (I live in one of the most expensive cities for real estate on the planet), and we co-parent and see likely too much of each other, but it is within a tolerable range for some of the benefits it provides our kids and the financial benefits. We will continue to separate gradually. If we separated now with a financial arrangement, she would have to pay me, as I lost my job.

No, she did not beg for the marriage to continue. She instead stuck to her guns in saying she wasn't sure if she wanted to be married, at least by my definition of what marriage is (which includes a romantic investment. She did not act non-chalent about it though. She acted hurt and as if she was the victim.

She had been going to therapy with me, but she hadn't been doing the mutual exercises, and resented me for trying. She had been using the therapy as a venue to further express her astoundingly rabid level of contempt - which was surprising even for me, and I'd been through a lot.

But what SHE was thinking eventually didn't matter at all. It had been established that either she didn't have a very good handle on her thinking or her behavior, and that the result was that there was no romantic investment on her part toward me. There simply wasn't any getting around the lack, nor the problems and work associated with trying and forcing it. That alone was enough to leave, eventually. She had a suicide card that she would play here and there, until she did it one too many times and her brother and I called the cops to pick her up, and she spent the night in the hospital strapped to a bed.

Not having sex with you is not her DOING something to you.
Remaining in a relationship that presents as romantic but isn't, and that is harmful to your well being, is you DOING that to yourself.
Having sex with someone who you know clearly doesn't want it, isn't much of a remedy to your problem, and she's been clear in how she feels.

The responsibility now goes to YOU to decide whether marriage for you includes romantic and sexual investment and expression.
For her, maybe it's not necessary to have that with you (and she knows she can get it elsewhere).
For you, it seems as though it is a pre-req in a marriage - a defining aspect of it.
You don't have that - so it comes down to what you are going to do about it.

Going to therapy isn't much of a solution. The first thing is really to decide on the goal of therapy. So is your goal to make do without the sex, or for her to have the sex that she doesn't want to have with you?

Honestly to me I don't believe in counseling when it gets to this point. She doesn't desire you and I got to a point that I didn't desire my H after years of rejection of course, but your situation is different because you still desire your wife. However with what I know today if I were you I'd be standing in the bedroom naked holding divorce papers and tell her to suck it well or sign the choice is hers. There is no cookie cutter solution but let her know she has 2 months to figure it out.

I have experience with BPD among my friends and family. It does cause irrational and impulsive behavior, and that might include cheating, but it doesn't seem to generally cause a lack of libido. It does cause problems in relationships, particularly with those close to them because they often attack and drive away their friends and family. In this case, you have been still invested and she is the one who has indicated a lack of investment - the opposite of that.

BPD isn't curable (though it can over a long time be managed to reduce some symptoms). The prognosis for treatment often takes YEARS to get toward a treatment and routine that works somewhat effectively. But that just manages the BPD - it won't create attraction or desire for a person.

Again, I don't see anything here that suggests the therapeutic intervention she's suggesting is going to work. If anything, it resets the clock and delays consequences while you assume the risk. There's no therapy she's suggesting that couldn't take place while you are separated - if you both choose a theraupeutic separation as opposed to a divorce. Then she assumes some of the burden to get back toward you and the marriage, as well as the financial risks, which are presently all on you. Even with therapy, the track record for success with this situation (if success is defined as a happy marriage) is very low, when it's gotten to this point.