I think you should meet with him, and before he says anything, just tell him "You know, I've been thinking, and this really isn't working for me anymore. I really like you, and we've had a lot of fun, and who knows, maybe we can get back together in the future, or even date every now and again if we'd both like, but I'd like to take some new directions with my life right now."
Do a "Robx" on him, mixed with a little "Pearlharbor." Pearl was exceptional at laying out for her boyfriend "Look, the boyfriend that I have in my life will be exclusive and committed with me. He will be considerate, X, Y and Z, and if that's YOU, then he will be more understanding that -- considering his past infidelity -- that he needs to make me feel safe again in the relationship. Now, whether or not that boyfriend is YOU, is COMPLETELY UP TO YOU . . . but this is what I need. Please let me know if you think you can do that."
In other words, you base this on what YOU need and want in your life, not on trying to control HIM.
