They are still married. His wife is therefore not "his ex".

I was just in your shoes not that long ago. I loved my girlfriend who was still married and living with her husband as roomates. If he "says" hes going to get a divorce unless he follows through with it then it counts otherwise he can say the sky is blue a million times. Once he does get the divorce it can take months to years to finalize depending on the assets they have together if any at all. If you do really want to stay then all you can do is be patient. I was probably a little too impatient that they were still together b/c it was more like a 3 way relationship, which was not very benificial in my eyes. If he really was serious about you then he would divorce his wife and this would be a non-issue. I wanted my ex to get divorced b/c I wanted to marry her, that didn't work out and now I'm in the back burner. There's always those that will tell you that this is a messed up situation you're getting into, and that may be true but it's YOUR situation nevertheless. I don't think mine was but did I handle it properly? Absolutely not. Does it kill me? Yes until this day it does. Trust me, I know how much it hurts especially that they were living together I was never number 1, and it hurts incredibly.

You're living out a cliche. If he wanted a divorce, he would have gotten a divorce. And if he cheats with you, he'll cheat on you. Everyone always thinks they're going to be the exception. That's rarely the case.