My 40yo mother is in a happy relationship with a 43yo m and still keeps her ex around because they are good (friends). The ex stays at my mom’s house on occasion and lives out of town because he is in a band and goes to while rehearsal in town. Recently he had my an ex stay over at my moms house while my mom was out of town. I came over to drop off some stuff and didn’t know she wasn’t home. When I used my key to get inside there was the ex of my mom’s friend sitting naked on the couch. I asked the friend if my mom knew she was there and he said no. I told him he should tell her or not talk to my mom anymore because it wasn’t right. My mom still doesn’t know he had her over and I’m conflicted to tell my mom about it because I don’t want her to be hurt by his decisions/ I don’t want to get in the middle of something that doesn’t have anything to do with me. Should I say something to her regardless?