This is a really intriguing thread, and I've been thinking a bit before posting.
I'm wondering if we can't really generalize about the OPs any more than we can about the MLCers. And perhaps the OP "type" depends on the "MLC" type. This seems to be the case in the sitch with my XH.
My XH is what Laura Day calls a "denial" type. Here is XH in a nutshell, quoted from Laura Day's "Welcome to your Crisis":
"You'll know that you are the denial type if something has happened in yor life that would floor most people, but it hasn't even fazed you. You don't think about it or mourn your loss; you simply move on."
This is my XH, and it appears to be Spider OW as well. Interestingly, this is what my T told me often happens: a person has an affair with a person of his/her own type, because that doesn't demand or require growth or accomodation. In contrast, a person marries someone of complementary type, because of the opportuntiy for growth. This seems to be the case with my XH.
Hope I haven't rambled too far afield. But my XH has the classic "qualifications" you mentioned, terrible unresolved childhood and adolescent abandonment issues.
