Hurtwife, I can see your point completely... If someone came to me and said they were having an affair with a married man who was still living with his wife and promising to leave her, I would also have serious questions and concerns.
However, having spent the last 1.5 years in an 'affair' and reading all the threads here on mumsnet from every angle (from the hurt wives side and the people 'committing' the affairs) I can only conclude that nothing is set in stone when it comes to why people are having an affair or as to what the outcome is... Of course I agree that an affair is essentially wrong, but they do happen for whatever reason and most of us who are in an affair are trying to get 'out of it' and sort things out one way or another...
Personally, I don't ever want to embark on an affair again and I know my partner has no intention either as it has been hell for everybody involved. I know there are men and women who get a kick out of chasing and having physical or emotional affairs, or who want to have affairs and at the same time carry on with their home lives as normally as possible but not everybody who has an affair is like that...
To be honest, when we started out, we both were trying hard to compartmentalize our lives too, and we tried 'just to have an affair'... but we were crap at it. And of course having an affair does not 'improve' your relationship at home, but we have both concluded that the affair was not the real cause of our marriages failing, that the affair may have sped up the process but that it was bound to happen anyway, whether it was in a year, or 5 years' time....
We both have been living a lie for a long time now and to assume it will never happen again, or that he would never lie to me, would be naive. On the other hand, in trying to make a decision or whether we should leave our marriage or not, and on whether to carry on with our relationship, we have both done an awful lot of soul-searching and I think we know ourselves a lot better now. We know what works for us, what we find important in a relationship, and perhaps even more important, we are so much more aware of the pitfalls in a relationship, the slippery slopes... One example is that we are a lot more open with each other than we ever were before and we will never leave frustrations or small disagreements to fester as we did in our marriages where we 'put up' with things (nothing huge but still points important to us) for years, just because we thought we could put them aside, because we told ourselves they weren't that important in the big scheme of things, 'nobody is perfect' etc.... Years go by, and you talk less and less about the things that are important, because you feel you are not getting anywhere with it, and at some point you realize you have grown into 2 completely different people with very little in common... So in terms of how 'sure' I am that the affair will work out? I am not, but I know I know myself a lot better and I will pick up any signs of 'trouble' a lot faster than I ever did in my marriage, and I know my partner will too... At the moment, I am not looking for 'lifelong' guarantees as I know damn well how awful it can be to be in a marriage which is meant to be for life when it really isn't working... So I really hope this relationship works out, and I will do my best to make it work, and hopefully we will live 'happily ever after' but I know there are no guarantees...