Does it matter what you believe religiously/about God?
If so, why does it matter?
If not, why doesn't it matter?
In general, beliefs shape behaviour, self-esteem, and relation to oneself and others. All of which manifest in actions. So, yes, they matter indeed.
But I also think that beliefs are only tenable if they concur with reality, and I simply don't know how to consciously hold a belief against my own judgment. I can tell myself that I'm the most beautiful, intelligent person on the planet, and it might make me much more confident and positive, but my brain will reject it because it's b.s. (I've actually tried stuff like that when I was learning self-hypnosis. It's a fun little exercise, and it teaches you one thing, if nothing else: Brains reject b.s.! lol.)
As to the god question, the mere belief that god exists, is probably pretty meaningless apart from maybe making you feel a bit better (or worse). But if you believe that there is a god who is opposed to homosexuality, or who punishes you for eternity if you dare doubt him... hooo hoy, it's going to make a difference!