AITAH for cutting my cousin off?

About four months ago, I cut off my(31M) 32 year old single cousin (his dad and my dad are 1st cousins) after I found out he had been flirting with my mom on FB messenger for over a year, from more than one account and while he was “with” a girl that was only using him. He would usually say stuff like “hey beautiful”, “hey hot stuff”, and once or twice he even said he wanted to take her on a date and kiss her even if it was just once.

At first my mom (age 54)seemed like she was trying to look past the flirting, especially given her (overly) sympathetic and forgiving nature. She feels bad because my cousin obviously has some issues. However, she eventually told him he’s too young for her plus she’s his cousin’s mother. She also suggested he get out there and find a gf. He said he doesn’t care about that and he wants her.

I eventually found out about this, on the 4th of July, when my mom was showing me a message from my uncle, when I accidentally hit something on her phone and it went back to the messenger Home Screen, where I saw a “hey beautiful” message from my cousin. I asked her about these messages and she told me that it had been going on for over a year, but didn’t want to tell his parents because she thought they would accuse her of flirting with him (she wasn’t and there’s still evidence of that).

I waited two weeks to go to his house to confront him. At first he denied it, but then he tried to say it was just a joke. I asked him does he flirt with all his friend’s/cousins mom and he said yes and he does it cause it was funny. That’s when I told him I couldn’t associate with him anymore not just because of the flirting but also his overall hateful, negative, and even bigoted attitude and he just said “fine I’m done”. I stopped at a nearby store and while I was there I went on my phone and deleted him off social media.

When I got home my mom showed me a message from him that said that he’s sorry for everything he’d said but told her to tell me not me not to talk to him anymore. He even blocked me on FB even after I deleted him.

Just so you all know, she and my dad have been divorced 18 years, but I believe he had crossed a certain line. I know teenage boys tend to have crushes on older women, and I would be more forgiving of that, but we’re talking about a 32 year old “man” here. Plus he would constantly apologize to my mom but would continue to flirt with her. AITAH?