I think that not wanting to lose a lovely lifestyle and split up a family with all the heartache that involves is a very legitimate reason for trying to make things work. It is NOT the soft option - on the contrary I think storming out is probably much easier, in the short run, but in the long term none of the issues that lead to the problems have been resolved. The children are left thinking: "all men are cr** like my dad" and so on.
Working through difficulties and accepting another person's imperfections IS part of a relationship. And don't forget, if you are going to subscribe to the wedding vow stuff: "til death us do part' means just that.
That is NOT the same as being a doormat, by the way. I personally think it takes more effort and courage to work thought problems in a relationship - yes even infidelity - than to walk away from them.
A little anecdote - friend of mine, 4 children, husband was an arse and she left him (justifiably so but long story). Life has been SO TOUGH for her - financially, emotionally bringing up 4 children with so little help from him (he blames her for the break-up).
With the benefit of hindsight she says she wished she had stayed in the relationship long enough to work through their issues and decide on the best way forward - so, if they had parted, it would have been on reasonable terms. She admits that part of the reason she left was to 'punish him' (and no he wasn't unfaithful - just an arse in other ways). He then 'punished' her back by withholding money and not helping with the children. And so on. And guess who gets to suffer, apart from both of them? Their children, who are the innocent victims in all this.
It has not been at all easy for her to get into other relationships and as anyone out there on the dating scene knows, the perfect man is not necessarily jumping through your bedroom window.
Sorry, have hijacked the thread and probably given a sermon. The point I am making is "chuck him out he is a cheating bastard", while completely understandable, makes for a very difficult long-term future. Work through the issues first, if at all possible, then decide on the best course of action.
None of us is perfect. Infidelity is crap, but then so are lots of other things.