OK so here's the thing.
I'm 18 years old and I'm dating a just turned 20 year old. We have been together for almost 2 years and honestly, I really do love him. But he has an older brother who is gay, and has been dating a 31 year old guy for like 9 years.. me and the 31 year old became really close because he's so sweet and easy to talk to... he's like my best friend.. but then I started to fall for him.. there's just something amazing about him that I can't explain.. he makes me feel so good about myself and I can trust him with anything.. but I didn't really think anything of it because he's gay, until one time when I was hanging out with him, and he kissed me. Like REALLY kissed me.. it was incredible.. I know it was wrong, but it felt so right. And now every time we "hang out" we spend most of the time making out.. but it's not just a physical attraction either.. we are alike in so many ways.. but the relationship is impossible because he is so much older than me.. he's supposed to be gay.. and he's extrmely close to my boyfriend... they're like brothers.. but I can't help the way I feel about him.. and I know he feels something for me too.. he's not the type who would just mess around with my head.. I know that for a fact.. but our little "secret relationship" has been going on for a few weeks now.. I really think I'm in love with this guy, but I don't know what to do about it.. I'm so confused.. because I haven't been feeling the same way about my boyfriend lately either.. I just want to be with this other guy.. HELP? =/

YOU need to talk with him about it. Ask him why things are like this if he is gay and in a relationship. Maybe he is bi and to a point he would rather have a girl than a guy.
You need to make a choice based on what he says. You need to be fair to your boyfriend or cut it off with him if you can't stop your heart from being with someone else.

You say this man would not mess with your head and yet he is cheating on his lover of 9yrs. With you.What makes you think he can be trusted when he would do such a thing?

This does not make him a paragon of virtue! Or someone who should be trusted.He is also stabbing your BF in the back,that is not a person worthy of trust.

You are young and I think his interest in you is flattering to you and you may be a little awed by his age and experience but I think he is using you for some purpose that I don't understand but I would avoid him like the plague.

I smell nothing but trouble here. For everyone involved!