How to tell if someone is a closet gay?

I'd have to agree leave the guy alone if he wanted to talk to you about it he would have. While there are signs that lead you to suspect someone is gay there is no certain way of knowing (one of the most camp guy's I ever met was completely straight while I've know a couple of really manly men who had more cock that a Thai prostitute). Even if you did know for certain how is that going to help if the guy does not want to talk about it. So I'd say back off it's not necessarily "a big problem" let him know he can talk to you about anything but stop trying to interrogate him

You don't "accuse" someone of being gay. Given your choice of words, it may be that you're being more curious than actually helpful. Why do you want to know? Do you have some kind of experience in helping people discover their sexuality? If not, then mind your own business and be the good friend you say you are.

Ok well this is one of those problems he has to figure out on his own and maybe does not want to talk about, and like you said could be very easily angered if you bring it up. Sometimes the best way to help a friend at times is by not helping and let the friend figure things out on their own. Unless it is life-threatening/he is suicidal, then it is not as big a problem as you may think. Especially if he isn't even bringing it up. It only sounds like it's a big problem to you based on what you've said about it so far.

If you want to keep the friendship with someone, I suggest you mind your own business actually. It's a very touchy subject to some people especially if they care a lot about what others think. And there is nothing wrong with someone being gay, its not a frickin disease, so he doesn't need help. And when the time is right that he is comfortable about it, then he will tell everybody if he is gay that is.

You can't really know someone is gay unless you catch them or they chose to tell you, and seriously, if he's not choosing to tell you, your endless asking will not change that, just irritate him. So stop. You shouldn't ask. If he is gay he will chose if and when to tell you. I have a few gay friends. Some are very open about it, others have only told me after YEARS of knowing each other. I never asked. If you ask and are wrong the guy isn't going to like it and if you ask and are right and he's not ready to tell you you will just stress him out more. Don't ask. Don't hint. Just leave it alone and be a good friend that he can trust, like you would be a good friend to anyone else. The only thing you might want to change is that if you ever make jokes (even if you don't mean to offend) about gay people or homosexuality or if you ever use terms in derogatory ways, you should obviously stop (you might want to rethink the implications of some of the things you say too - for example in your question your words imply that being gay is a problem and that gay people need help. You also say "accuse" of being gay, like being gay is a bad thing or something wrong). Just be open minded, sincere and trustworthy and if he is gay and wants to talk about it, HE will. If you are asking questions and hinting about it all the time, you are acting like you care less about him and are more just generally curious and want to know for yourself. So stop and just go back to being a good friend.