Clinton cheats because he is a horndog,,,in my opinion. He would cheat on anyone.
The interesting question to me is why he married her. I think he has a deficit deep down, a disorganization, which made him know he needed an iron willed person to keep him sane. Plus he knew he wouldn't be a "husband". He is hooked to her, not married in his heart. He knew he wasn't giving up his catting around ways. The man is just a compulsive womanizer.
Theirs was certainly a marriage of convenience. SHE needed someone w/charisma to get her in the door to power because she is lacking in it. (BTW nobody seems to ever report that they shacked up before marriage and she paid the rent.)
I suspect that you are probably right but I would also think she triggers a lot of it as well.