I'm not sure breaking up is the right thing, actually. On the one hand, I can definately see how you'd feel he had done something 'shady' during the time you were together (I think that's natural) although, I'm curious....does he have the same suspicions about you? Has he ever voiced concern that you might have done something with someone else, or does he assume you didn't? I also can imagine, if he didn't do anything at all, his getting pretty fed up with the accusations, even if they aren't outright voiced, but winnowed in with leading questions.

In any case, I'd err on the side of caution--yes, you are young, but you have invested a great deal of time in this relationship to just walk away now. I, too, recommend couples counselling---sit down with your bf and have a heart to heart...acknowledge that you have been feeling insecure lately, and remind him that the break up was very difficult for you. Suggest both of you see a counsellor as a way for you to overcome these concerns...try to make it sound as proactive as possible, so he doesn't have any inclination to go on the defensive.

Once both of you get an objective ear, from someone who is familiar with this type of situation, I think both of you will feel better about what you'll want to do going forward with this relationship.

Take care