Most Helpful Girl
They usually cheat if they feel their needs aren't being met with their current bf. For yoinger girls they might just want to experience what its like with someone else. For experienced girls or younger girls, it might be because the guy no longer makes her feel attractive - eg, he hugs or kisses her less, the foreplay diminishes, he stops telling her she is beautful and starts complaining instead (so uses negative rather than positive language). It is rarely about having bigger muscles
Most Helpful Guy
No, I'm buff as you can see, I'm smart, funny, decent cock, I fuck like a gorilla and my wife is deeply in love with me, but tonight she's going to fuck some other dude, she meets other random men a few nights a wee, and I meet other girls. It's nature, don't conform and be fooled by modern societies perception of a functioning relationship dynamic. Monogamy doesn't work, your ex is proof that. If you like eachother then take her back and just do what you are supposed to do.
But yes, hit the gym, it triples your female interest.