Love is so irrational because a lot of it is held together by feelings. You know all the reasons why you shouldn't be together. Your feelings are just trying to catch up to that. There must have been some buttons that he pressed that make you miss him. The fastest way to get over someone is to make yourself busy so you don't have the time to think about things like that. Time heals all and eventually your feelings will catch up with your reasons.
If you simply must talk to him though, tell him that it's over and you would rather he didn't call. You can be friends later on once you are completely over him.
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~