My best friend came back after being gone for 2 months

She made so many friends there and she has means to contact all of them and i wish she didn’t. She was at a mental hospital and you’re not supposed to stay in touch with people you meet there but she didn’t care so i just acted like i didn’t care either and that it was funny. I mean i really want her to have more friends cause i geniuely love her but i’m so fucking insecure for some reason and i hate myself for it and i’m way too dependent on her i can’t do anything without her or being able to tell her or her supporting me. Before i met her i had no friends for 3 years and that’s where i spiraled into depression, anxiety and social anxiety. When i met her 2 years ago i thought i could live my life again since i’m only 17 and everyone kept saying i was wasting the best years of my life which i think is total bullshit but i see their point and i thought so too at the time. Today i talked to her for an hour and thats when she told me everything about the people she met there and god i felt so useless. I feel like now that she has so many friends she won’t need me anymore i want to kill myself so bad but i don’t want to do this to her but if we start to talk less i geniuely won’t know what to do with myself and idk i feel like i don’t deserve her and its all my fault and i don’t know what to do cause usually we just vent to eachother and talk everything out but i can’t at tell her any of this because i dont wanna make this all about me but i just relapsed and cut myself more than i ever have and i dont even know why i feel like this and i hate myself i wanna die i dont know why my whole world revolves around her i feel like if we’re not friends then i have no more purpose and this hit me even harder because i’m on meds for a few months now and it was all getting better but now i dont know anymore i hate myself