He said before to you that he dont know if you r gonna be the one for him rite? after years of r/s....and then he comes back again? feeling remorseful???? or purely wants lust?
1) if you really want to patch back with him, please be careful not to repeat the same thing again. at least consider birth control methods. And you really really need more time to tell whether this man is really worth being together.
2) if you think such man cannot be trusted and do not want to get hurt again, leave him. Without leaving the past behind you can never walk out to see the sunshine. There will be someone who is there to love you. Just takes time to find and meet the right person worth your love.