So my now ex cheated on me with one of his friends from work. I know she has a boyfriend she’s been with and I don’t know if I should tell him what happened between them. I don’t want to do it out of revenge but my ex and her had unprotected sex with each other and I feel like he should know especially since they (my ex and his coworkers) always hang out and still work together. I also know she hasn’t told him. Any advice ? Should I tell him ?