I think it's better to forget about him if he's so fickle. Living with him will be a continuous torment because you will not be able to be sure of him. Moreover, if he "sees" his ex, then he is also a cheater.

It is very sad that you have to go through this. But it may be better that it happened now than when you were already married. And so you will not waste time on it.

I am sure that you will have a better man who will appreciate you and who will be sure that he wants to marry you.