Well, we had a talk

I reckon I could mount reasonable counter arguements to the *roadblock issues* you see Sister choosinghappy , in partic the financial ones, but this isn't the time or place for that.
Rather, I think this is a time to congratulate you on the balancing act you have been able to manage thus far.
You seem to have adopted a pretty pragmatic approach to the whole picture, and that pragmatism is a great tool to have in your box of tricks.
It will serve you well in this trying environment.

When you get around to that information gathering re the financial implications of divorce, check out also levels of government assistance for you as primary carer of your kid, and what the kid is entitled to in their own right in regard to gov. assistance, subsidised child care and suchlike, education supprt etc etc.
In my jurisdiction, all sorts of gov. assistance for the disabled is available (with plenty of hoop jumping to access it I ought add)

An affair as solution indicates that you are still framing the problem of your marriage as a lack of sex, rather than how your husband's aversion to sex with you makes you feel.
Having sex outside the marriage tends to shine a bright light on what's lacking at home, further illuminating a comparison to how you feel on excursions with your paramour who desires you, vs how you feel with your husband, who avoids you. The lesser investment your paramour has in shared history, hardship, stakes, compared to your husband, rubs salt in the wound. Invariably, it shows that a near stranger is more likely to want you than this person who knows you. Resentment on the home front increases.

If the affair spills - either as a result of increased vigilance and suspicion on your spouse's part, sloppy forensics on your part, your paramour's part, or increased vigilance on your paramour's spouse's part, then you run the risk of a furious and betrayed spouse deciding to wreak maximum vengeance, or possibly even becoming despondent and depressed and nuking their own career. It's pretty common for work performance to dive in either a devastating infidelity AND a divorce, and data indicates it tends to hit men harder than women.

Medical insurance, especially for special scenario with kids, is a sound, practical and reasonable consideration. 
It's possible your spouse may feel the same way.
It's possible your spouse may also lose his job or his insurance at some time.

In my own separation, we have chosen (so far, a couple years out) to live apart but to remain financially blended and to support the household as a financial unit, including with medical benefits (as we have some of our own). We are both invested in the notion, at the moment, that the children are the priority and meeting their financial needs is the priority. There's no guarantee that a spouse might arrive at similar thinking, but I can say with conviction that had I chosen to separate upon discovering my wife's cheating (as opposed to her telling me and trying to work it out), I was completely out of my right mind then, and likely would have attempted to inflict maximum harm, and try to put maximum distance between us as fast as possible, possibly to the family's long term detriment.

An insight the family counselor gently tried to nudge us toward:
Whether you are together or apart as husband and wife, you are going to remain a family as co-parents for a very long time. Perhaps the rest of your lives.
Upon reflection, I think he was trying to get us to reframe "the relationship" as something independent on "the marriage", and changeable.
The "marriage", such as either of us defined what a marriage is, was effectively over, and had been for years.
The "relationship", as something undefined, continued.
It's worth your time to break down the benefits that you associate with the marriage into smaller chunks - such as financial benefits - and to question the likelihood of such benefits continuing in one form or another in a separation.