Maybe it seems obvious that a person willing to hurt their partner by withholding sex has control issues, but I always thought it was an intimacy issue, not a control one. I thought the sexlessness was about him not wanting to be touched (by me anyway) and not wanting to let me in emotionally. It’s taken years and putting a little distance between us for me to see that in my case at least, he has a huge issue with control. No wonder he’s freaking out now that I’m stepping out from under it.
I suspect that most of the time the intimacy issue is a control issue. It is an unwillingness to feel vulnerable or exposed, or to allow things to get 'messy' or 'out of hand' in a way which is felt as potentially dangerous. Keeping sex functional and unemotional is the first step towards doing that, and refusing sex altogether is even more effective. Especially when you have a partner who will let it go on for years and still try to be nice about it. Control freaks are basically all about managing their environment as tightly as they possibly can because they are shit scared of what might happen if they don't.
The same things are occurring with my divorce. my W's 4th attorney is immediately labeling me as uncooperative, without a single fact to back it. You can see the fear in my W.of loosing power and control over her tightly managed environment. This revolves very much around money. She wants to get divorced and expects to not pay one penny in alimony.