Thanks. If I could not be here, I would not. However, I am glad this place exists for those of us in this predicament.
add'l info

Our “live in” separation has us alternating weekends on who goes out and who is with her our children.
My biggest issue, that I know I need to let go, is fidelity. I object to the idea of dating others as well as any physically intimate contact. That is one of my values with which she totally disagrees because “we’re separated, whatever happens, happens.” The fact that there is an OM, and this will be her weekend to go out, totally gets me to. Tips for how to detach?
I have started reading and exercising regularly. Actually requests that she has made of me for awhile. I’m now doing it and enjoying it for me, not to simply “win” her back. Furthermore, I am drinking weight gain drinks, as I initially lost 10lbs with which I cannot afford to lose. I have always been skinny / “wirey.”  I have also started to reconnect with friends (talking, texting, and spending time with them). I’m trying to discover old or new hobbies. Nothing jumps out yet.
Everything we’re going through makes sense She had an abusive childhood, parents had a horrible divorce, she had a child early; and then we met. I come from a “normal” childhood, dad worked and mom stayed at home. I’m using the word “normal,” very loosely as I don’t like to use the word. A huge part of my inherent problem is that I’m too nice, I want to help everything and everyone. I need to start with myself; and yet at the same time am struggling with being too much of a “friend” due to our circumstances. Again, I do not want her to think I’m being the same “too nice” guy to “win her back.”