Why did my mom's friend do this?

My mom is 41 (but looks 30) and she has a friend named jenna (not actual name) jenna is 60 (but looks 49) ok so jenna is my mom's boss and they've been friends for years( my mom has been married 13 years with 3 kids and jenna is single with no kids) so today we were at jenna's house (without my dad) and when me and my brothers were in the living room, i walked into the kithen and saw jenna rubbing the tops of my mom's boobs.....and then she gave them a light smack.........i was astounded cuz i thought this was completely innapropriate....... Jenna seems like a lesbien cuz when we're at her house...her and my mom will go upstairs and say they're fixing the computer and they wont let anyone in. She also is obsessed with my 7 year brother........i feel like i should tell my dad but i dont want my parents to get divorced.......what should i do?????