I don't know how to have a healthy relationship with people

I've dealt with my depression for many years. Ineffectively, at least. It started becoming a major problem when I went to college, and my best friend went to college just an hour away from me. We were inseparable in high school, always laughing and talking. We were almost like sisters. Now, I don't see her a lot and it's greatly affected me. I've become extremely insecure about whether she'll find new friends that she would rather be around than me and when she got a new boyfriend at her school, I became even more insecure and even jealous. We only ever text and see each other maybe once a month, but it's taken a toll on me mentally and emotionally. It's gotten the point where say things that I justify as my feelings, but they make her feel guilty and ashamed. Like why she can see her boyfriend everyday, but we never get to hang out or even call. She's become so busy and we never have time hang out and laugh anymore. Her boyfriend has noticed how I affect my friend in a toxic way (I see it too and it sickens me). What used to be such a cheery and fun-loving friendship has turned sadness and shame...and I feel like it's all my fault. I told my friend that maybe it would be better for her if I just walked away from our 5 year friendship, but she would be sad. I fear if I can't find help managing my anxiety and depression and breaking my manipulative behavior, I'll sabotage a cherished friendship and crush someone I care about. I'm desperate...