My friend is a real womanizer and he has no problem with women who use him to cheat on their boyfriend ( he won't do married woman though ! )any way he has five rules to know if a woman his cheating on some guy .

1- She's no longer as needy as she use to be.

2- She no longer gets angry at you.

3- She's being secretive about her whereabouts

4- She places the focus on your  part of the relationship.

5- She showers you with love though sex ain't getting better.