How can I find out if my boyfriend is cheating?

This is a tough one but I would say maybe meet him after work a couple times or have him call you when he gets off of work. If he remembers to call you and tells you what he is doing in these late night excursions then it is a good sign he is not fooling around on you. I also don't think it is such a bad idea to suprise him every once in awhile by showing up at his work when he is getting off.

You are his girlfriend so he shouldn't be ashamed to be seen with you, and should want to spend more time with you. I also suggest sending him text messages to check in on him when he is out really late, just to make sure he is ok. Unless you have a real cause for concern, I wouldn't approach him directly and ask if he is cheating, sometimes you have to be able to be trusting, and sometimes you have to trust your instincts.

This is one of those times when your instincts might be telling you he's up to no good, but he might just be hanging out with his buddies and drinking. I would just give him the benefit of the doubt for now, unless you see other evidence that he is not being faithful. And also don't snoop around his e-mail or computer, that would be a serious breach of trust.