Not my story, but one of a married bi man who I used to hook up with regularly. He openly shared his story with me without much prompting. It's one that is probably common.
His wife completely shut him off from sex. It seemed to be that she wasn't interested in it anymore, but of course he still was. He tried to hook up with a woman he worked with who knew the situation, but she said no and suggested he try looking on craigslist for it. He started posting looking for women to hook up with, but was getting a lot of messages from guys who said if he was striking out, they'd suck him off. He didn't give in at first, but eventually did. He was having no luck with women and decided "fuck it" and let a guy blow him. Initially it was a way to just get off, but then he started doing it more often letting guys blow him. He started to realize he was interested in men, and then tried blowing another guy. Turned out he loved it, and it kept going from there. First fucking guys, then eventually getting fucked by them. It made him realize how much he was into men and turned into basically a total bottom. At the last time we talked, he said he hadn't had sex with his wife in five years, but had more cocks in his mouth and ass than he could count.
From others I've talked to, it seems like that is the common trend.