If they accuse you of cheating, insecure about you earning more money, they want to check your phone but hesitate to show theirs, if they are uncomfortable with your clothes, if they use alcohol or drugs as excuses for bad behaviour, if they don’t speak well of their ex’s, if they can’t treat their mother’s or sister’s right, if they have objectified any of your friends through jokes, if they seem obsessed with body count, if they are pro hook up culture, if they follow Andrew Tate, if they enjoy typical “wife jokes” , if they want the wife experience but not ready to actually wife you up, if they watch too much porn, if they have a toxic friends circle…
Many red flags above but usually people or in this context mostly men cheat when they have lost power or respect, it’s mostly a way for cheap relaxation. It’s extremely sad that society uses sex as a means of escapism.