Kristin, I've ended 2 long-term relationships in my life (the first 4 years, the second 7). Despite the fact the relationships were unhappy at the end, both times the boyfriend did not take it well and did not want us to break up.
Despite knowing I did the right thing, I felt a lot of guilt, because I hate the idea of hurting anyone, even people who have hurt me. With both relationships I had fleeting thoughts of going back, because I just wanted the hurt to stop.
My advice is, if you don't want to hurt your ex-boyfriend, don't even bring up the topic of reuniting unless it is something that you actually want, and are in the right mindframe to consider. Think about it, if you go back, it's more than likely you're going to end up in exactly the same position as you were before, when you decided to end it. Judging by the fact you've broken up several times, you know this already.
I don't know if you have a counsellor or therapist, but it may be something you want to consider.
You can, and you will, get through this. The way you feel now will not last forever!!! Be kind to yourself, and look after yourself.