If a man is in a long-term relationship, he might think that he is not attractive to other women anymore and he will do everything in his power to prove himself wrong.
That is the moment he will start chasing other women and having affairs with them.
During that time, he will start taking care of his looks more than usual and he will neglect his partner.
He will probably lose interest in her and start finding other women on different dating sites.
The adrenaline will make him feel desirable again and he won’t want to let go of that feeling.
The problem is that it is all in his head and because of his different behavior toward other women and their feedback, he will gladly continue this chasing game.