Just because a person does not want to have sex does not mean they are gay.......but it's one possibility. Other possibilities are asexuality or he's got a low love level or he's not in love with you.
In my situation, my husband was never really interested in physical intimacy, from day one. We didn't even kiss until the 7th date, and that was because I initiated it. There were many things that made me think he was an in-denial gay man. Too much to get into here. Even a couple of friends tentatively approached me, afraid of causing offence, and suggested he might be gay. They were surprised when I agreed that he might.
Once he woke up in the middle of the night, and busted me watching (straight) porn in our home office. He was so upset.
It was such a reversal of roles, he, acting like a naive, offended housewife, and me, assuring him that it was just harmless entertainment.