What to do... what to do. I don't want to have him come back to me and tell me these things again only to continually date his girlfriend. It's awful!!
Have you considered setting a more firm boundary or going darker? I had a similar dynamic w/ my WAW and it came to a point where it was not emotionally healthy for me to see her so often because it would trigger feelings of hope and expectations whereas she seemed comfortable with flirting and being friends.
Give yourself some space and you may find that you detach further emotionally from him and put some more power within yourself. You can always re-engage more at some point down the line.