Wait a minute. That Guy cheat on his girlfriend with FL (she was too stupid to don't realize any of the signals - don't met the parents, don't get invited to his place etc. - but okay) and at the same night discovers that his girlfriend cheat on him too. Motherfucker, you just reap what you sow.
Also, ML did it right. FL really is the type of person who would accept him back after all the bullshit (she didn't get any of the red flags, easy to manipulate).