Personally, having been cheated on myself, there is one and only one reason why someone cheats. Because they are selfish. They selfishly think they can get away with it. They selfishly think they deserve it. They selfishly blame any shortcomings in the relationship on their betrayed partner.
If they feel like something is lacking in their relationship, there are an infinite number of OTHER more MATURE things they could do instead of cheat. Including ending the relationship if it's really that bad.
Saying that they cheated because they felt their needs weren't being met is such a cop-out and a blameshift to the betrayed partner. If the needs weren't being met, then why not communicate said needs and talk to your partner instead of sticking your dick (or letting someone stick their dick) in someone who is NOT said partner.
Saying "I couldn't help myself" is also bs. Yes they could. They just chose not to. The affair partner doesn't have magical powers and cast a spell on the cheater. There wasn't some giant magnet that pulled the cheater into bed with the affair partner.
And if the affair partner is fully aware that they are the OTHER PERSON, then it doesn't matter if they are more or less attractive than the spouse. A dog turd is a dog turd. Some dog turds have pink icing and sprinkles on them, but it's still a dog turd.
I didn't care what my ex's affair partners looked like. I didn't care if he "felt he was lacking in the relationship." What I cared about was the fact that instead of acting like an adult and TALKING TO ME, communicating his needs or being open with me, he chose to stick his dick in 6 other people. Then had the nerve to tell me it was my fault.
No. It was entirely his. He could have been mature. Instead he chose to be selfish and immature. So in the end, does it really matter what the affair partner looks like?