Lil said to LG: Don't disappear from the R in an attempt to be "nice" and give her lots of room. It's okay to act like you care what happens to the relationship. In fact, it's really important that you be present and visible, kwim?
LG asked: Lillieperl, or anyone else, could you talk more about the idea expressed above?
I don't remember exactly what I was replying to when I said that, but I think it was sounding to me like you were trying to be Mr. Nice Guy, not too demanding, giving her lots of space to think things over, etc. My advice was "don't disappear," by which I meant don't be too accommodating, compliant, easygoing, etc. Your W has committed a major transgression-- not that I'm advocating burning at the stake or anything-- but you need to Be There, Want Stuff, Ask for Things, Have Opinions. I don't know if this is any clearer... but identify what you want and speak up. If you don't want her to move out, then say so. If you want the two of you to go to counseling, say so. Don't just let her wander off while she figures out what she wants to do. Don't be passive.
This may not be any clearer.
Something about your R contirbuted to conditions which led her make herself vulnerable to an EA or a PA. It does not happen unless the one having the A opens the door a crack and lets someone else in. I'm not saying it was your fault. SHE made that decision, but she did it because something was lacking in her interaction with you. In the past when I was vulnerable to an A, the way I would describe my internal state was "starved for attention." It was when my partner neglected me. That didn't make it right, by any means. IMHO it's important that you can SHOW her that you understand that you contributed to the conditions that made an A appealing. That she got your attention, and that you have changed and you are prepared to change MORE.
And cac is right: I agree that you've divulged too much personal information about your sitch. Real names, university names, city names-- suggest you cease that immediately. Way too easy to find people.