Reading the comments of the last few posts, I've been wondering about that issue myself. Fortunately, my W has not engaged in certain overt behavior with OM. As far as I know, and I'm pretty certain about this, their time spent alone has been very limited. There is no phone contact, etc. But after reviewing Tim's sitch and some of the others, I wonder to what extent I could put up with that. I mean, I am being supportive and understanding of her emotions, trying to be more of a friend than a husband and employing the other DB principles, but I do believe that if certain lines were ever crossed, I would establish some boundaries rather quickly. I haven't read anything in DB or DR that advocates being a doormat.
TMU, again while there may be some similarities in your sitch and Tim's, as well as mine, there are also several major differences as you have outlined.
Just my two cents worth.
"Achieve success, but without vanity; Achieve success, but without aggression; Achieve success, but without gain; Achieve success, but without force." Lao Tzu