This is a pattern I've seen repeatedly.

Guys find themselves desperate to get laid, and that desperation comes across in all of their interactions with women, who don't like feeling that they're being treated like a vending machine, which leads to the guy being rejected for reasons that he doesn't entirely understand.

He gets in a relationship with someone, finally, and everything is great for a while. Then he realizes that women are talking and flirting with him more than they ever have before, and isn't sure why, but he enjoys it. He doesn't understand that, because he is in a relationship, he has stopped being desperate and weird, and is now actually having real conversations with women about mutually interesting topics.

Surrounded by women that are (seemingly) available, he either breaks up with his SO, asks for some sort of open arrangement, or tries to cheat. Unfortunately, for reasons that he still doesn't understand, as soon as he's available for sex, women start being turned off by him again (if not to quite the degree they were before) and, again, he finds it difficult to get laid.

From here, guys often fall into some incel-style evolutionary psychology explanation for things, regularly cheat on everyone that they're with, or gradually becomes aware of the pattern.

If they become aware of the pattern, they can begin to manage it and reduce the desperate, salesman vibe that they give off. As they become more confident and relaxed, it becomes clear to women that they're perfectly comfortable going home alone or just being friends, which allows them to have more meaningful relationships and, incidentally, more sex with people they like.

Anyway, thanks for coming to my TED Talk on the origin and mating behavior of the involuntarily celibate.