At some point, if you really, truly can't trust her, maybe that just means you really, truly can't trust her. Heading off an affair that would be a mistake is one thing, as is fighting for the marriage, but if you fight for the marriage, bring it back to life and then have to spend the rest of your life monitoring Facebook, then you haven't made it all the way back yet.
I'm pretty sure people were having affairs before Facebook . . . Anna Karenina is mostly about Friendster and Myspace, isn't it?