It's not a good sign that he'll cheat on someone instead of being honest and working on the relationship.
He might say his wife is a horrible person and try to put her down, but again, you don't know.
If he has a pattern of not choosing the right woman for him, that doesn't bode well for your relationship.
You don't know the nature of his relationship with his wife.
His wife is leaving again soon and they're technically separated, but I know they obviously still talk.
I wouldn't consider myself "the other woman," but it's just a weird situation to be in.