There have been many discussions about OW on these boards, none of them very flattering, but one consistent factor that emerges is how many of them are actually mentally ill - by bi-polar, emotionally unstable, schizophrenic and so on.
I think they attract the MLCer, and are attracted to them. RCR talks about negative energy, and it does make sense. If you say 'The OW is crazy' it sounds like the angry wife, but truly, so many of them are extremely disturbed. And of course they so often play on this as the MLCer tries to break it off - suicide threats, and so forth.
Don't worry about 'driving them away' The MLC has a life of its own, and I have come to believe that thiere isn't a lot we can do except be true to ourselves, and as kind as possible to them, while maintaining your own boundaries. Almost anything we do is subjected to weird misinterpretation. If we stand for our marriage we can't accept reality, and if we initiate divorce proceedings we can't wait to get rid of them. If we want to get everything sorted out legally, short of divorce we don't trust them, and so forth. It is like a distorting mirror.
