My mom slept with one of my childhood friends

Me and my mom just started talking again a few months ago and I find this out. Me and my mom have had a very rocky relationship our whole life. She was very absent, a drunk, we never got along. We recently started talking again and things have been okay. But with her things don't stay okay for that long. One of my friends who I've been friends with since middle school was talking to me and wanted to tell me some things. He told me him and my mom had sex years ago while we were still in middle school. They had sex on a few occasions. He at the time was 13. I didn't believe him at first but he showed me text messages between him and my mom that were recent. She was basically telling him that she hopes he didn't feel like he was manipulated when they were sleeping together and hopes they were on the same page. He was telling her that he feels kind of weird about it now and she was saying how they didn't really do anything wrong. He was a teenager at the time not a child. It was just disturbing. What makes this all even worse is my mom wanted my son to have his 15th birthday at her house and said he could have his friends spend the night. His friends are between 13-15. Idk if she really wanted to do it for him or to try to sleep with his friends. Idk. All I know is im disturbed. My mom was never really a great mom but I had no idea she was like that.