I want to ask some people's opinions of this but it's gonna be a long story!

Early last year I dated a boy for a few months, now we're both 16 and dated for 3 months so really not serious at all. But he made me super unhappy, he criticised everything about me and everything I did, so I ended it. A month or so after we went our ways I bumped into him again and decided to stay friends as we were friends for around 5 months before dating. But then the day after I saw him I got a message from a girl in America (I'm in England) who I have literally no idea who she is, Saying 'I need you to cut the shit with ***** what you're doing is a crime, I know your dad left but that's no excuse to treat him like shit and I was like WHAT THE FUCK!! He's clearly spreading lies that I'm a messed up girl cause my dad left when I was a kid, on top of that he told all our mutual friends I left him because I'm a lesbian. So I got really mad and told him I want nothing to do with him.

Now, my mum has always been a right kiss ass to him, he use to call her 'mum' she use to call him 'son' and they still talk and do that!! I told her all the lies he spread, showed her the message I got and the horrible things he said while we were 'dating' but she still wants to meet up with him. And I really don't understand why? For a start he's 16 and she's in her 30s so a bit of a weird friendship anyway, ( if that was me being friends with a 30 y/o guy she'd lose her shit!) but is it just me or is it weird that she wants to hang out with someone that told people her daughter is doing something worthy of jail time (which I really am not!!!)?! I also have a new boyfriend who I've been seeing for just over 6 months and she makes no effort at all to talk to him or try to like him, but she wants to hang out with a guy that talked to me like a piece of shit?! 😳 I've also told her I don't like her talking to him buuuuuut she does anyway.

What do you think, am I right to be mad or is she being fair just wanting to stay friends with - I quote from her: 'a nice mature guy'?!