Depression from love

I don't really know what to do so I decided to make my problem public in hopes that I will find some comfort. Since last fall I've been feeling very depressed. There was this girl I knew for a long time which I used to go to dancing lessons with. When she broke her leg I helped her get home for a month and we spend a lot of time together that way. When I build up the courage to ask her out she said yes but that she needs to leave for the holidays. When the holidays ended she told me that shes sorry but that she already got with someone else. Even though I tried not to we slowly fell out of contact. Things got worse when my only friend slowly moved on to his new friendgroup and I became even more isolated. I am very introverted person and find it difficult to make new connections. To this day I still time to time see her because we share similar way home and we still have warm conversations like we used to and I get happy like a dog seeing a familiar face but the feeling quickly wears off and I feel horrible the days after. I find myself in places in which she can be, Im wasting my time waiting, haunting those places like a ghost hoping she'll be there. I've even learned her favorite song on guitar. She was the only person I truly felt seen by.
Recently my situation got even worse because I've become so depressed I started having trouble sleeping. I tried taking melatonin but the outcome was unsatisfactory. Im sleepless and if I fall asleep I often times experience dreams about her. This sleeplessness makes me think about death so often. I do not want to inflict any selfharm but I cant stop thinking about who would missed me or how would certain people react. I want to draw it but I alway stop myself. I wanted to reach out to someone for some advice what to do in these situations.