Nate - so sorry that you're going through all this but I really have to echo what everyone else has said.
I get how hard it is - but if all this is going on now, marriage is only going to make it a thousand times worse. It will hurt so much more emotionally (not to mention financially!!) if this happens again in a year, or 5, or 10 - or more likely, repeatedly every few years. Do you really want to live with that? Do you want to have kids someday? If so - do you really want this woman to be their mother??? Step back a minute and set the feelings aside, and look at your life 10 years from now. I think it'll help you get some clarity. Then you can deal with the emotional "fallout" from that clarity.
Me 35, H 38; Together 13.5 yrs, M 7 Bomb 1 10/07/06 Sep'd 1/14/07 - 4/15 Piecing: 4/07 - 9/07 Bomb 3 10/11/07: Never loved you, let's separate 2/08 slowly improving 7/08 Piecing (7/25/08 rings back on!!) Current thread