Boyfriends mom hates me 🤗

So I’m 17 and my boyfriend is 16. We’ve been dating for 2 years and a couple weeks. Let me start from the very beginning. We were very young when we had first started dating around 12 and 13 years old. But we broke up because.....We were young and didn’t understand what a true relationship was. We found our way back to each other. We had a couple of offs and ons like any young couple who doesn’t know how to communicate does. We’re way past that now. But it seems like every time we’re doing good and having a great time in each other’s company, his mother constantly has to talk shit about me. And this has happened a lot and I’ve just been dealing with it but I can’t anymore. I’m sorry but his mother is literally the fakest person in the world. She smiles in my face and then talks shit about me while we’re on the phone together. He’s a total mamas boy. I mean he disagrees with her when it comes to me. And she always does things to get a reaction out of me. She’ll tell me he’s cheating on me (He’s had problems with this in the past) which then I believed but I’ve just stopped believing anything she says. There was only 1 reason I can think of that she has to say things about me but it was a long time ago. We were caught having sex by my parents and they told his mom and this was 2 years ago. I believe that in her head she thinks I’m a slut and that I’m trying to trap her son. And if that was true I would’ve done it by now. Otherwise I haven’t done anything to her. She treats me like shit. My boyfriend stands up for me but she keeps doing it. I just want someone to tell me why moms do this? As if talking badly about who your child loves helps them in anyway at all? Like please help. Because it’s getting to be really stupid. We both come from Christian families but she’s a total hypocrite judging me. It’s a shame that I have to be the bigger person to an adult who doesn’t know how to be an adult. She’s extremely childish.