It can sometimes be difficult to know if a boyfriend is happy, particularly if your boyfriend isn't skilled at communicating. Since both parties in a relationship need to be happy for the relationship to stand a chance for long-term survival, you should approach your boyfriend if you feel he may not be happy in the relationship. While there is no way to fully know if your boyfriend is happy, there are signs to look for to help determine the state of your relationship.
Look for signs your boyfriend isn't happy. These signs include a sudden lack of interest in intimacy, frequent desire to be alone, inattentiveness toward you, insensitivity to your feelings, or frequently engaging in activities without you. These may be signs of something else going on in his life, but they are likely signs his feelings for you are changing.
Invite your boyfriend out for a special night. Choose something he enjoys doing and follow it with dinner. Be yourself and make the date romantic. Watch his reaction. Look for disinterest or an eagerness to end the date. If he doesn't respond to something you've set up specifically for him, there is something going on. It may not be that he is unhappy, but taken in the context of other signs, it's a good bet he might be.
Communicate with your boyfriend. If all the signs are there, direct communication is the only avenue. Ask him if he is happy. Sometimes his response to the question might be all you need. If he is sincerely confused you would ask him such a question, he is probably happy in the relationship. If he tells you he is happy and asks you why you think he isn't, take his concern as a positive response.
Encourage him to share his feelings with you if he tells you there isn't a problem with the relationship. Tell him what you've noticed in his behavior and ask what might be going on in his life you can help him with. If he has any issues and decides to be open about them, this will help ease your mind that the issues aren't with your relationship. All that will be left after that is to give him the space he needs to work through his issues and help him when he needs you.