Hey TG,
I am new here but know exactly what you are going through. I just posted a reply to Cupowater about the same sort of thing.
My ex was exactly as you guys are describing here. Notice i said ex? It took him 5 1/2 years but eventually the flirting turned into a ONS. And that was it. The dealbreaker. He has had 6 g/f's in the last 5 months. Basically he will be with anyone who will look after him and let him drink. It is so humilating to me to realise how unspecial i really was to him.
I am here now in an effort to understand how i let myself go through this and to heal myself. I am sorry you are dealing with this. Its hell on earth.
Hugs to ya