Little Engine - I get that sick to my stomache feeling frequently. I feel the same way you do about fighting or giving up the fight. My fight was trying to convince her to stay with me, that she is making the wrong decisions - that kind of fight just backfires
Instead, It is all about DBing and GALing... You need to live your life - that is what is important.
You are in a fortunate (?) position where your W is confiding in you when things are bad with OM. That is, you are the friend who is there for her when she is down (even if you do not want to hear it)... That is the best position to be in to regain your relationship over time.
Keep your head up and learn to enjoy your life (As I am trying to do somewhat unsuccessfully).
Me:40 / W:33 / D:3 T:7.5/M:4 D Day: 1/24/08 Legal Separated: 6/12/08 BF who sleeps over: confirmed 11/10/08 Suspect BF pre-dates D Day