Ex is with someone new, how do I deal?

We have been broken up for a little over a year and I still miss him a lot. I would get really lonely and reach out about every month or so even though I haven’t seen him in 10 months. I just would want to talk and feel less alone. Last time we spoke, at the begging of this month, he said he would call me back in a few days. He didn’t which led me to spiral thinking he hated me or I did something wrong. So I texted him asking for clarification, if he didn’t want to talk anymore that’s fine but I’ve been so scared he hates me. He responded saying he has been seeing someone for a few months and we can’t talk now or going forward. I just feel crushed, it’s not that I wanted to get back together but losing that connection hurts. Now I can’t stop crying, I’ve been crying for days. I feel like I don’t matter and wonder if he still thinks of me or if I’m completely out of his brain. How do I stop wondering and caring if he cares about me and that I meant something? Will I be completely forgotten?