You are in a tough spot with your boyfriend. The first thing I would do is ask your boyfriend if there is anything that you are doing--without realizing it--to make him doubt your fidelity.
Ask him if he thinks that you are doing anything to lead men on? Does he think you are a flirt? Obviously, if you find out that you are doing something, then you will want to stop that right away.
I have a strong suspicion that he isn't going to be able to point out anything that you're actually doing to set off his jealousy; and even if he does identify something and you change that behavior, he is likely going to continue being jealous. Why? Because his jealous is a smokescreen for the real issue that troubles him.
His real problem is fear of abandonment. You see, his jealousy is really telling you 'I'm afraid you're going to run off with another man and leave me in the cold.' To heal his jealousy, he needs to own his deeper fear, identify the childhood trauma that set the fear in motion and then work through the feelings associated with that trauma.
You can test the waters to see if he's open to delving deeper into his soul by saying something like, 'Honey, I have the sense that you are really afraid that I will end up leaving you.' If he agrees with that statement, then you could go a bit deeper by saying, 'Have I given you any reason to think that I would want to leave you?'
He'll probably say no. Then you could say, 'You know, I've been doing some research and I've found out that the things that hurt us as kids often reappear in our relationships as adults. So, if someone abandoned you as a kid, or threatened you with abandonment, then you would be afraid that I would leave you too. Can you think of who hurt you like this when you were young?'
If you've gotten this far in the conversation, you're on the road to healing the problem. If you can't navigate the talk, there are a couple of options for you.
You can read my book, Till Death Do Us Part (Unless I Kill You First), which has an entire chapter that starts by describing common relationship conflicts, such as jealousy fights, and then shows you how to decipher the exact childhood conflict that 's causing that fight. The book then goes on to show how to heal the wound.
You can also have him do my Psychological Check-Up, when I finally get it online (soon, I hope!), which will pinpoint his wound and give him steps to heal it. Last but not least, if you need more one on one help, you can contact me in my private consulting division.
Don't give up. This problem can and will be healed.