I want to preface this by saying I do not condone Patrick's behavior & believe he should have to deal with the consequences. Having said that, I think Robin is partially to blame for alot of it & all of them (including Steven & Matt) have a hand in Lisa's spiral into Lunyland. This woman showed signs of being a nutjob right from the start. Who leaves a coveted spot at a major metropolitan hospital to go to a little hickburg in upstate New York, where they only know one person? Especially when that person is a happily married ex-boyfriend with a child. The only possible reason is that she wants to get back together with the ex. Yet none of them, except Maxie thought it was odd or predatory.
Who's the first guy Lisa latches onto in this town full of hot, available men? Patrick's brother. A brother Patrick is very competitive with. Then, when it doesn't affect Patrick like she'd hoped, who does she pick up with? The hotshot new doctor that Patrick has an antagonistic relationship with.
Then, when Robin starts to get a clue what Lisa's up to, how does she respond? She goes off to Africa for a month, leaving her husband & daughter. A daughter she swore she'd never leave again when she was recovering from PPD. She, once again deserted Patrick. It's almost like she was daring him to cheat.
As for how Patrick has handled this situation from the point of realizing the mouse was off the wheel, the first thing he should have done was either come clean with Robin or deny, deny, deny. He waffled too much, giving Lisa all the power. He definitely should have gone to Mac when Lisa broke into the house. If he decided to keep lying, he should have let Lisa tell Robin they slept together & make her prove it. Naturally, she couldn't. Case closed. Call Mac, get the lunatic locked up & keep it zipped up when the wife's away.
As for Robin constantly saying Patrick would never cheat...Can you say Leila? I'm sorry. I can't imagine a woman as insecure as Robin not being at least a little concerned about leaving her husband alone with a woman who's been circling her husband for month, stroking his...er...ego. The writers dropped the ball with this bad remake of "Fatal Attraction" & Emma is not a bunny so they better not even go there.