As you pointed out, you both have been less than honorable in the ways you have treated each other. Your boyfriend showed very bad judgment 6 months ago. I have no idea if it was the last gasp of an old behavior or if it means that he is still willing to throw everything with you away on a whim. You need to talk to him about it. For this relationship to have a chance, you both have to agree that all the old game-playing is over and that you will both do everything in your power to be worthy of the other’s trust. You then each need to give the other the gift of a new trust.
Yes, a gift. In cases like yours where there is so much negative history, rebuilding trust requires the ability to forgive and to risk being hurt yet again. If you really can’t bring yourself to make that leap with him again, you owe it to both of you to break up. You both made some big mistakes when you were young. Now that you’ve matured, you need to find someone you can fully give your heart to and so does he. Maybe you can do it with each other. But it may be that too much has happened for you two truly forgive each other. Listen to your own feelings and trust them.
I wish you well.