Yes. While there are other possibilities, his consistent presence on gay meetup sites suggests that he's gay.
So yes--I will go out on the limb and say he's likely gay. And I will also say it likely does not matter, because sex is the least of your worries.
This has nothing to do with you or any perceived deficits. It has nothing to do with your relationship.
Sexual orientation is on a continuum. It's not as black and white as we tend to think. Being gay--or bi, or anything because we all have our individual quirks and preferences--is not the primary concern here, except inasmuch as you want and deserve a partner who wants to be with YOU.
Rather, your BF's behavior worries me for reasons that have nothing to do with orientation and everything to do with the fact that secrecy and lies erect a barrier to emotional intimacy that makes it impossible to have a genuine loving relationship with respect as its foundation. (There are disease concerns that are heightened, as well, if he is having unprotected sex with a higher-risk population.)
Gender preference/orientation is on a continuum. Many people successfully have committed relationships with partners who are gay or bisexual, but who have chosen to commit to individuals outside their usual demographic.
But no one successfully has had committed, mutually rewarding, emotionally intimate and fulfilling relationship with a liar and a sneak.
And THAT is your real problem.
That you've reached this at 15 months in is what worries me most. (It also gives me the most hope, because you can still relatively easily extricate yourself.)
At 15 months, you are in what should be an exciting honeymoon phase marked by exploration of one another's dreams, desires, preferences, goals, and yes---the things that make you tick sexually--with one another. Instead, he's already seeking sex on the side--in a particularly sordid way that speaks volumes about his ability/desire to form real intimate relationships.
Really, orientation is only a bit player here. He's showing you he can't be a good partner to anyone--at least not at this point in his life.
And there is nothing you can do to mold/shape/change this. He is who he is. He's shown you. Believe him.
YOU get to define how you'd like the rest of your life to look. Is this it? Because I can virtually guarantee you this is the way it will be--and that it will escalate. A man who only says, "I'm sorry; it won't happen again" is a man who's not committed to real change.
The best predictor of future behavior is past behavior. Can you live with this forever?
[This message edited by solus sto at 9:40 AM, July 24th (Thursday)]