I think you are spot on and I was going to reply with the same thought: in many cases cheating is not just about sex at all, or even primarily about sex. This was my personal experience when I cheated (serially), not to mention what leading experts in the field say about it:

"All over the world there is one word that people who have affairs tell me. They feel alive." --Esther Perel

Plus fucking hell, that was endlessly, tragically funny.