How can I prevent losing a friendship?

I (19F) don’t really have friends. I have one friend (20M), but we’ve been growing distant lately. I know losing friends is inevitable, but I really don’t want to lose him. He recently got a boyfriend, and while I’m supportive of his relationship, it feels like I’m losing him. I’ve brought up my fear of losing him, but I’m not sure he fully understands where I’m coming from. He’s reassured me, but it hasn’t helped much. I’m sure it’s just my insecurities, but I feel like if we keep drifting apart, I’ll lose him. What should I do? I also feel like if I keep bringing up my fear of losing him, he’ll get annoyed, and I don’t want to be a burden. I’m nearly at the point of giving up on making friends. Should I just accept that I’ll be lonely forever? I don’t want to be alone.