To answer your question 'is it too late?' and if not 'how to get your boyfriend to give you another try' we need to face a deeper issue. And unless we do this, things will never work out for you with this guy or with any other guy for that matter.
It sounds to me like you live with the fear of abandonment. (You said yourself that for the longest time you wouldn't let yourself feel because you were afraid that he would leave you eventually).Many times when we have been dumped as kids, we end up fearing that the same will happen in our adult relationships. This fear often leads to relationship destructive behaviors like you describe (cheating, etc. )
But why would a person who is afraid to be dumped act in such destructive ways? You probably didn't know that your unconscious mind thought that it could protect you by arranging to dump him before he could get around to dumping you--kind of like dying by your own sword. Unfortunately, this kind of defensive maneuver doesn't protect you in the end, it only makes your worst fears come true--you get dumped eventually.
So, in order to get this guy back, you need to admit to him your deepest fears of abandonment and explain to him that your mind was playing a trick on you (dumping before you could get dumped). If you are honestly willing to admit these fears of abandonment and not act them out in such destructive ways, and your boyfriend really believes that are going to do this work, he may try again. If he doesn't, I 'm sorry for you.
But this has been a learning experience, and if you take my advice, you will be able to find and keep a new relationship. The key for you is to stop the 'I'll dump you before you can dump me' pattern. You need and deserve a love that sticks. Face the fear, don't try to escape it, and you'll be fine. My best wishes to you.