She said "divorce me and make it right" because then she can say you BOTH wanted this and BOTH realized that it was best. She wants to pretend you have already worked on things and tried and have come to this realization that it won't work. Problem is she knows you both haven't tried together yet. If you divorce her, in her mind she will believe you both agreed.
She really may mean what she says about knowing she has to cut ties with OM but doesn't know how to do it. I was there. She feels she loves him, she is addicted to what he gives her.....it is hard to go through withdrawel and hard to see someone that you feel you love hurt. That is what she is going through. Help her through this by saying you know it is very hard, but you need her to do this.
I don't believe the whole she needs to leave to see if she misses you. I don't believe that at all. She will miss the OM right now, not you. That's just the way it is right now. What she needs to decide is whether she stays with you and tries her hardest and gives it her all, or if she divorces you and goes with OM. Basically there are only two choices. If she needs time alone...she can have time alone at the house you both live in with the kids and can stay away from OM. YOu can be there to help with the pain or give her space or whatever, but she doesn't need to leave to figure all that out. If she leaves the home, I believe she will be done. It is soooo hard for her to leave as it is...if she jumps that hurdle she won't come back. That's my thoughts anyway.
The letter.....I would adjust it according to what I just said and I wouldn't go on and on about how you will be there to help her move, etc. NOOOOOOO! Remember, she wants you to make this easy on her. Do not.