Seeking advice on ending a relationship that goes against my faith

Alright, so I'm in this situation where I've been chatting with a guy, and it's starting to feel like something more, even though we never officially called it anything. I only know him from real life and we've talked once, but mostly it's been texting. Honestly, I'm not proud of any of this except that I'm trying to stop something that isn't right according to Islam. He's into stuff that I can't really talk about here because it's not in line with Islamic values. Plus, he'll disappear for days and then come back apologizing, saying he was dealing with things. When I try to help, he doesn't even reply. I also found out he was talking to his ex not too long ago. I'm really worried that if I stop talking to him and say it's over, he might get upset or even do something worse, like tell his friends or my family. Even though it's wrong in Islam, I'm scared about my reputation. I deleted our chat from his side so there's nothing left against me. He seemed nice at first, but nothing lasts forever, and more importantly, this goes against my religion. I want to focus on my studies now and stay away from guys and all this because it's clearly haram. If anyone has tips on how to tell him this gently and nicely, I'd really appreciate the advice. Jazakallah khair in advance.