This "you'll only drive them together" is a myth and b.s., in my opinion. In almost every sad, horrible situation on these boards (and I read all of them, even if I don't post on them all), the infidels are already "together!" And they're getting to do it with damned near the "blessing" of their spouses who are afraid to confront them and fight for their marriages.
No, you can't "force" someone to not have an affair. But you can damned sure fight for your spouse, and let them KNOW that you will fight for them, and not enable the behavior. I'm not saying you do that personally, addie, but many who advocate the "Whatever you do, don't spook the infidels!" approach do.
There's a big difference between GAL and DBing, and being a doormat. I realize that there are two schools of thought on this, and reasonable people can (and do) disagree, but I just don't think you should ever base your disagreement on the false illusion that you'll "only drive them together."
These people are already together, and actively setting the agenda and the timetable for the exits from their marriages.