I like to call it "the poison apple" - once eaten it's difficult to get the toxins out of the system.
Great analogy! The infidelity is what makes Future's situation so much worse; thanks for pointing out that I wasn't clear enough. What I was hoping to suggest is that I believe we need to assume the best IF we want to work on our M, even as bleak as I think an affair makes it. If the other person screws up in response to our actions, and we still want to work on the M, then we need to change our actions the 2nd time round.
At the same time, we should look for the what ifs and prepare for the ones that would help meet our goals/needs (not necessarily theirs).