How long have you been dating?
What kinds of problems are there other then sexual?
Who is having the sexual problem?
What kinds of problems?
Stress is a huge issue for men and sexual function........when a man is stressed it will effect his ability to feel desire as well as the ability to get or maintain a erection. The good news is this is seldom a permanent issue and with treatment and time he will be able to go back to the way things were.
I would suggest that he set up a appointment with his doctor. His doctor can go over some of the causes of his stress and prescribe medications if needed. He may also want to consider eliminating the stress that is going on in his life. Stress can effect many aspects of his life including this and make him very sick so the sooner he eliminates some of the stress the better he will start feeling.
I would suggest that you do not push this issue right now......a mans ability to mate is a serious issue and can cause emotional issues as well. So it is best to not cause any additional stress by making a fuss about this. Let him know that this is the biggest symptom of stress ad suggest he see his doctor. Then give him some space in this department. Do not push for sex, talk about sex, or ask for sex. Keep your relationship on a love level instead of a sexual level.
You can help out by trying to eliminate any stress that you can. Try not to argue with him or press him on important matters right now. Now this does not mean that you stay clear of him.....just make life about cuddling and being there for each other emotionally right now. When he feels he is ready he will try again.......just try not to put it out there that you are waiting. When you discuss the stress let him know that you understand and this is no big deal. Let him know you love him and that sex is just a part of your realtionship.....not the whole thing.
Try to keep in mind that at some point in your life you may go though the same thing and try to put your self in his shoes. Would you want him to make you feel bad or push you? No so do the same for him. Men are far more embarrassed about issues like this then women so try and be understanding and non demanding.