Thanks for writing to Alterheros. You tell me you're very close to your best guy friend, you guys joke around by touching each other or flirting. He has a girlfriend, but you like him as more than just friends. You're not sure if you should tell him how you feel.
It's hard to give you a straightforward answer, but I will try to help you with the situation. First of all, do you know how your friend feels about homosexuality, or bisexuality? I think the answer to that might influence what decision you should make. For example, if he has already made blatantly homophobic statements (possibly ones alluding to violence), the risk of him rejecting your feelings, or perhaps your friendship all together is higher. If this is the case, you should think about how important it is for you to free yourself of this secret. Honesty if often a good thing, but if you think he will probably react negatively to your feelings, then you have to assume the consequences of that action.
Also, do you know how committed he is to the relationship he is in? That's also something that might have an impact on your decision. You might want to think about how you would feel if he is interested, but that leads to him cheating on his girlfriend. I mean that your values, your relationship with the girlfriend (if there is any), the way you want your relationship with your friend to advance, these all have an impact on the situation. On how you will view the things you do now and yourself, in the future.
I can't give you a yes or no answer, mainly because I don't have much information on your friend and the way you guys interact. Has he ever seemed more serious (as in he likes it too) when you were joking around, or have you noticed him looking at you at odd moments, has he ever mentioned finding a guy cute or hot? This might be hard to hear, but you probably have more information than I do to figure out how he will react.
I think the main thing you have to think about is if telling him how you feel is worth jeopardizing your friendship. You will most likely feel hurt if his feelings don't match yours, even more if he does not want to stay friends. Would you be able yourself to just be friends with him? To lose the relationship all together? I'm not saying all this to discourage you from telling him, or to insinuate that he is not interested, but being rejected is never easy, and I wouldn't want you to get hurt. If you do think he might have feelings for you, then yes I strongly suggest you be honest with him.
I hope this helps you to analyse the situation a bit better and I wish you luck Jake, whether you decide to tell your friend or not.