Wot? an ex stays with him on weekends? Strange.. i wouldn't trust them.
I understand of how you felt. Jelousy, but then you are not in the right position to feel that way for a reason that you haven't been meet in real and you are not committed to him yet. Accept the fact that this is only an online dating, and you don't know the real score. Perhaps he lied to you or he lied to his so called ex. She might not his ex...they might still together and she has no idea that her man is playing while shes away.
Well anyway, its just my point of view.
You don't know whats going on there. If shes an ex and they still see each other physically..well theres more possibility that they can patch things up and back on track, and you are the history.
I think moving on is a key.