If it were me, I would leave now, but since the two of you seem to be sticking it out because of the children, then your only course is to hold out for 6 years as you mentioned.  Until then, I suggest you work on building up your confidence and self-esteem by working out, keeping busy, learning new things, joing interest groups, and focusing on your boys. The fact that your husband refuses to go to counseling together means that he is not serious about the two of you working things out together, and that he still wants to hide things from you, and I get the feeling that you know this already.  You asked what will happen to the marriage once the boys move out of the house.  It's simple.  The marriage will end, and you will move on.  There are men out there who are faithful, and looking for emotionally intimate relationships - and YOU CAN FIND ONE.  In fact, I don't see why you can't put out a personals ad right now, as a married woman looking for friendship with a man.  Better yet, as I said earlier, by joining interest groups, I'm sure you can find a male friend to confide in, and perhaps in 6 years, something more than that.  Your options are endless if you just open yourself up to them.  Too many people trap themselves in relationships that are not healthy and not fruitful.  Not every marriage is worth saving.

Please read this article - it has some very good points: http://www.huffingtonpost.com/2013/08/11/cheating-spouse_n_3721907.html