So I watched seasons 1-3 of madmen and I'm a bit confused as to why Don Draper cheats on his wife. I always thought when married men cheat, it's because they are unhappy or they just don't have a sex life with their wives. Although Don seems like an unhappy person, he seems to be happily married to his wife who he has a healthy sex life with. It doesn't seem to be out of entitlement because he does try not to cheat on her, it also doesn't seem like he's a sex addict and he really seems to care about his mistresses so is he capable of falling in love with more than one woman at a time or what? It's just sad to me that a woman can be beautiful, have a sex live with her husband and be loved by him and still be cheated on.
Don was happy being married to Betty. He wasn't happy that his marriage to her was built on a lie. I think Don knew that Betty only loved the idea of him. They both actually had a mutual infatuation for each other, but they were never in love. Notice how throughout their marriage, they were very affectionate and had a sex life but not much more than that. I do think that Don really cares about Betty though, because he tired not to cheat on her and hated himself for doing it. He also was hurt when she left him ( the first and second time) However Don's cheating has nothing to do with Betty or his marriage to her. It's a problem he has because due to his traumatic childhood, he cannot commit to one woman and there is nothing Betty did or didn't do to keep him from cheating on her.