Men need emotional support sometimes just as women do. However, they may not need it in the same way. Men often need time to try to sort through a problem themselves before reaching out. Many women reach out to their closest confidants when an emotional situation arises. When you are trying to be there for your boyfriend, realize that he may not want or accept the same kind of support that you would want in his situation. Your best bet is to tread lightly and be patient with him during his tumultuous time.
Let your boyfriend know up front that you love him and are there for him. Tell him that you are there to listen, not judge, and that you are willing to lend an ear if he needs someone to talk to about his problem. Then let it go. Don't pressure him to talk to you. He will come around and talk to you when he is ready, most likely after he has had time to consider what to do about the problem.
Give him space. Your boyfriend might need more alone-time than normal, depending on the severity of the issue. Know that this doesn't reflect on you; he just may not want to spend time with anyone. Don't push yourself on him, or he will only push you away, which will create an entire new set of problems. This doesn't mean that you have to stop talking to him altogether, but perhaps lower your expectations for your time together for a little while.
Cut him a break. If your boyfriend is extremely stressed, the last thing he needs is for you to be overly critical or to pick fights with him. Often couples fight during high-stress situations, and if you take a look at the fights that you've had during these times, odds are, they were pretty pointless. If a fight is worth having, put it on the back burner unless it is about something truly serious, like infidelity.
Do something nice for your boyfriend. Treat him to a date or send him a plant for his apartment. Flowers and plants aren't just for women. He will likely appreciate your gesture and will feel loved and cared for. It's possible that your small gesture may even persuade him to open up to you. With a small gesture, you are still showing your support without putting pressure on him.