Sometimes people who are gay don't acknowledge that until they're older and finally able to deal with their sexuality.
BUT they tried to make a go of it, they had sex with their wives, they had children, they made love often and with vigor...they tried to prove they were straight. They wanted to be straight and not have to admit they were gay and "come out" and live with ridicule, discrimination, and more. No one chooses to be a way that causes others to hate them and look down on them.
Everyone wants to be normal, fulfilled, happy, and accepted. Now that more people are receptive of gays it's easier for those who are attracted to the same gender to admit this and live their lives like they want.
Again, these people work extra hard at their marriage to try and prove they are straight and they are NOT gay. They want to make their marriage work so they won't be gay. They sometimes live their whole lives in a marriage and are content, they may never act on their secret desires.
The few people I've known that ended their marriages to live a gay lifestyle have had normal marriages for the most part. When one of my college friends decided he was gay he finally told his wife. Then once she had accepted it they told their kids. Then he moved out and started living a life he thoroughly enjoys. He's been with his partner for nearly 20 years. He is happy.
Another friend, my college roommate, was so in love with his girl friend. He worked so hard to make every right choice to build a strong healthy relationship with her. They broke up my senior year. He hit rock bottom and it broke him. He struggled with so many things for a couple of years. He finally admitted he was gay several years later. He was a good christian man and wanted with all his heart to not be a sinner. That's how he'd been raised and how he felt for a very long time.
He has not been to church since he came out. He still has a hard time with it all and often says he's glad his mom died before his life changed. He's slowly coming to terms with it all.
Being gay and being in a marriage that isn't working is hard for everyone involved. I truly don't think what you're going through is this situation though.
Having no sex drive has nothing to do with sexuality. It has to do with hormones and how the brain is wired for sexual interest.
I have known one woman who was asexual. She was very upfront about it. She was married to a really nice man and had 4 kids, was expecting #5. They had a good life. She was a very nice person too. She hadn't had a celibate life before marrying this man. She said she'd never needed sex, she'd never really enjoyed the whole aspect of it either. She actually said that was a half hour should could live without...
She had gone to the doc, got tests, and everything was normal inside. She just had no interest in sexual contact.
I asked her why she married, if she could go out, date, have sex if she decided she wanted it, or could live without it completely. She said she wanted to have a family, live with people she cared about, have a normal life. So she submitted to her husband any time he wanted to make love, she got pregnant when they decided to have kids, etc...she did her "duty".
She didn't resent her lack of sexual interests. He didn't make her feel bad either. He accepted it was her issue and that it wasn't him. It was totally her issue.