You know, it’s interesting how characters seem to change on rewatch. The first time, I swear I LOVED her, she was my favorite, and I supported her, understood and defended her the entire time. I thought she was a miracle. On rewatch the second time, I started to despise her and was shockingly siding with Don, even when he started cheating. I suppose he should have just ended it the minute he realized her true colors, which I don’t think were at the bday party or the sherbet fight... I think it was when she was got her commercial part - well when she asked Don to help out with it. It’s made kind of obvious in the last scene of that episode but I think that WAS the defining moment. Before that I think Don still had some hope even if doubts. And I don’t even think that it’s about Megan doing what she wants - I don’t think THAT’s what bothers Don.. I don’t think he cares that she’s not the traditional housewife, he’s not interested in that and he truly likes Megan’s freshness, and her quirky modern ways. I think what turns things sour for Don is when he realizes that Megan might have just used Don and painted herself to be much easier to be with than she actually was, only to achieve her ultimate goal and what she really only cares about: acting. I think it’s clear that she actually truly had been ACTING all along until then. She really IS a great actress! She played the part to get all the way to the top in Don’s esteem until she was there and then she threw her tantrum. She certainly wouldn’t have pre-marriage, pre-perfect apartment, pre-getting the job as copywriter and everyone’s adoration in the office. I noticed how incredibly fake that scene when she quits and starts crying is - well pretends to cry. She did not care at all. Remember when she said: “I really would like to be doing what you and Peggy do!” And there are a bunch of subtle moments before she gets to the top that point us in the direction of her fakeness. I really don’t even think she ever loved Don. She loved that Don loved her, that’s all.