Your repetitive thoughts may be a way of you trying to rationalize what had taken place. Perhaps you're hopeful that things can be helped that he can change hence, not letting go of the thoughts.
It sounds like you had gone through a lot with him. It may not be a wise idea to rekindle a friendship with him (he had moved on, and hopefully you would too) Some partners are just not meant for one another (and you're correct- people have to have more things in common to have a good solid relationship)
You would want to make an effort to see the situation objectively, redirect your thoughts onto something else (whatever it is that makes you feel better and happier) The mind accepts whatever information you send to it. When you catch yourself thinking or obsessing about your ex, try to immediately shift to thinking about anything but tea. It will take practice but the brain is flexible.
Why not start dating or at least looking into such an opportunity? You can do anything you want.
Emotional Unavailability : Recognizing It, Understanding It, and Avoiding Its Trap - Paperback (Mar. 11, 1998) by Bryn Collins