I met someone in August 2020 (when we met I was 16F and he was 17M, i’m now 17F and he’s 19M) and we immediately got along. We got along so well we decided to try a relationship but we eventually ended it since he lives about 2 hours from me and it was just hard. I still had feelings afterwards and I would constantly message him a lot wanting to talk to him and wanting validation but he was so distant. Whether he was rude or nice to me or replied or didn’t reply it would constantly affect my mood.He acted shitty towards other people too and it just hurt me to see. 
I eventually did the right thing and stopped talking to him for my own  mental health and a few months later he texted me on my birthday so I gave him a second chance but after my birthday my life went downhill. I was in a really bad place at the time and I wanted him to be there for me so I became obsessive and I texted him so much and blew up his phone and he told me to stop a few times but I didn’t and he blocked me in June. 

A few weeks ago he texted me apologising for what he did and told me he was diagnosed with BPD a few months ago and explained everything. He also told me he’s now in a relationship but since then we’ve been facetiming a lot until like 3am in the morning, when we first facetimed we spoke about our relationship and how he felt so guilty for what he did to me and whether or not we could work out in the future. He texted me the next day telling me he was sorry about the night before because he was too drunk to be talking. He couldn’t remember anything but we both agreed to pretend it never happened so then it was morally better. Since then we’ve spoken on the phone til late at night and when we facetimed a few days ago we fell asleep together by accident and when he woke up before me at 7am he didn’t put the phone down or anything. However he has brought up his girlfriend now and again ever since we made the agreement to pretend that conversation never happened. I can feel myself becoming attatched again and I don’t want to get hurt and I also know he has a girlfriend so I’ll probably do the right thing and move on again. 
He’s very on and off with me, he’ll show me a lot of affection and then for two weeks after that he’ll seem cold and distant with me, and it hurts a lot. 
I’ve also wondered for a few years whether I myself have BPD although I’ve never been diagnosed. 
I know that I need to move on but the whole situation has always confused me and hurt me so much and I never know what to make of it. 
I just need advice, thanks for reading all this if you read all the way through.