If Don does cheat, it would be an interesting reveal of his psyche. Someone suggested that Don actually doesn't want the typical American housewife. He's attracted to women with a life of their own and a job and work they do. Betty was a working model when he met her. There was the artist chick. Then there was the department store owner gal. Of course, Faye is the ultimate of this type. And Megan made him happiest when she was showing her skills in advertising, and he seemed to go along with her acting as long as there was some real hope to it. Now, her mother tells Don that he has to take care of Megan, and so Don gets her the job. So, if that makes Megan less autonomous and if Don turns to cheating then it may be that he actually needs an independent woman to be satisfied.