Freedom, you really handled that conversation so well. Well done on keeping all those codie tendencies in check!
I too found out that STBXAH had another woman just waiting on the sidelines. I thought they were just friends - I trusted him completely. Hah. At the time I was angry at myself for being such an idiot. Talking this through with my counsellor, I'm still really angry that he betrayed me but I have learned that such unconditional trust is a dangerous thing. I won't ever trust anyone again that way and that's probably a good thing. He knew I would believe him despite the tell tale signs.
Now that the initial hurt has faded, I can see the positives. I'm kinda grateful. I think that if she wasn't there for him to latch onto then I would have had a whole lot more hassle from him than I did when he left - and I had enough for him to cope with! It also meant that I had no hope for our marriage. Infidelity is a dealbreaker for me - cast in iron because of my father. The marriage was over, no ifs, not buts. 'All' I had to focus on was putting myself back together.
I hope that you too can find some positives from this once the sting of betrayal has faded. It hurts like hell, I know. My counsellor really helped me - do you have a counsellor to talk to about it?
And congratulations on quitting smoking! I too quit cold turkey 8 years ago and it was really hard. I decided that the cigarette wasn't going to be the boss of me and just stopped ('kay, I had tried on and off to quit for about 6 months before using patches etc).