Ostrich,
It's been a struggle for me to get to this point as well.
Everyone here says "concentrate on yourself" and I would try. I really would! But so many days I didn't even have the energy to get up and cook a meal, much less do something nice for myself.
Then, suddenly I realized that the majority of "concentrating on myself" was in my thinking.
While I was thinking my "what ifs", I was thinking them of HIM.
What if he changed this, what if he changed that, what if he hadn't slept with her, what if he hadn't told her he loved her. (gag)
At some point it truly dawned on me that "concentrate on yourself" could simply start with the "what if" being about ME.
What if I filed for divorce?
What if I bought a little house with a garden?
What if I saved some money and traveled like I'd always dreamed?
What if I got my hair cut and a pedicure and some new clothes?
What if I just worry about MY shit for today.
What if I don't think about him and HIS PROBLEMS today.
I began to separate my problems from his and to understand that this marriage cannot be worked on right now. Period.
Play the what if game for yourself. Even if it's just a wild daydream that may never happen (one of mine was a deep, emotional conversation with Jonny Depp-hey, he's single!)...give yourself permission to think about yourself.
I did, and it's truly changed my focus.