Don, out of a need to break through the facade that he has created, cheats on his wife a lot. In Season 2, he dealt with the consequences by being put out of the house, before he rediscovers the love for his wife, and convinces her to give him a second chance. The season ends with a happy moment, of Don placing his hand on top of Betty’s, a symbol of them back together. Then, Season 3 starts out with Don, although more hesitant, back to his old ways, cheating on Betty with a flight attendant.

The producers didn’t want to make a big deal of this. Season 3 wasn’t going to be about Betty leaving Don because he’s cheating on her again. But every action must have consequences.

So after Don returns home, while laying in bed with Betty, enjoying the comfort of his loving family (something he previously took for granted), his daughter finds a pair of wings in his suitcase. They are the flight attendant’s. “Daddy, are these for me?” Don pauses. Glances at Betty, watching for her reaction. Internally demons are screaming at him. “Yes, of course,” he says.
Betty doesn’t react. She trusts her husband now. That night Don doesn’t sleep.