Having trouble letting go, need some advice

[MBDTF]

Hey guys
Never thought i would do this but at this point I think I should ask for help. If some of you are willing to read this and tell me what they think I would really appreciate it.

I met this girl in the summer of 2015 at a music festival. Her group sat with me and my two friends, and when our sights crossed i knew smthng was "different". I was a few months away from turning 18 at the time, and had few experiences with girls. We talked a lot and spent the rest of the evening together. We live in the same town, so we started dating shortly after. She was my first girlfriend. I fell deeply in love after a few months, and she did too. The first year / year and a half together was magical and it is the best part of my life even though it hasn't been that long since then. When 2017 came out she started going to college (im 1 y older than her). Things didn't change at first; she met new friends, and I was really happy for her because she had been through some shit with her old high school friends during the first year of our relationship, and I did my best to support her through that. Turns out one of the friends she made shared a flat with her ex. For the whole school year she told me I didn't have to worry about this guy, and she did not lie at that time. She never cheated. Her seeing her ex so often was bugging me a lot, but I put up with it because she was happy with her new friends and things were still going well. He was her first boyfriend, and one day (in like may 2017) he told her he regretted breaking up with her. It ****ed her up. She still loved me a lot back then, i least I believe so, but she wasn't sure whether she had feelings for this guy or not. It hit me like a truck, but we eventually got through this.2017 was not "as good" if I can say so. Before and after that, we were fighting a bit more etc. But we got through this first thing and I still loved her as madly as ever. Summer started, we went to a festival (stuff we loved doing together and have done multiple times during 2 years), then i worked for a month and saw her a bit less. Then she went abroad for a month for the holidays. At first everything was ok, but after 2 weeks she started replying "i'm coming back soon" to I love u, I miss u texts. I thought it was weird, but stupid and blind as I was I didn't see the big sign. Then I just noticed that it was really bad and told her to call me immediatly and explain. She told me she didn't want to do this over the phone and wanted to see me to talk, but I was scared shitless and insisted. She broke up with me over the phone, saying she didn't loved me anymore. We both cried our asses off. She came back home a week later, a week I spent in kind of a daze, waking up a 4 pm everyday, barely eating. We met at my place and broke up. This is the greatest pain I've ever felt in my life. We talked and cried for 2-3 hours. At some point she tried to kiss me on the cheek because I was totally panicked; I've never felt something as painful as that kiss. broke out in tears, almost screaming. She just didn't love me anymore. Blind as I was I realized months too late the trouble she was having. i love(d) her and cared for her so much, and was trying my ****ing best to make her happy everyday, so the thought she was having this kind of problems didn't cross my mind. Maybe I just didn't want it to. She was crying when she was about to walk out the door, I asked her to stop crying for our goodbye (holding it in was a nightmare for me); she blinked a bit and stopped and looked at me with eyes I'll never ever forget. I fell in love a thousand times over at this moment, but we hugged and she left. I lost it seconds after she walked out the door.
I sent her a few messages in the two days after that, but tried to get my shit together and didn't talk to her for a month. Then I learned she ****ed her ex. She did one month after the breakup. I went crazy, insulted her 100 times by text, apologized, asked all the questions that were running through my mind. My heart was broken already and this just ****ed me up very very badly. Like, our whole relationship seemed like a big ****ing lie. I told myself she lied to me for a year about that guy, which I think is partly true, and felt betrayed. I never lied to her even once, even for the smallest thing. It was very important for me. the fact that she did not tell me everything, that she didn't look me in the eyes to tell me "we need to fix this" hurt me really bad. Since then I started sending messages to her every two weeks/ month or so, talking for a day or two each time. I know i shouldn't do that but I think about whether our relationship really means/meant something to her or not 24/7. She went out with that guy for a bit but it didn't work out. I doubt they'll get back together knowing their history. Because I asked, she recently told me she is kind of with a guy right now.
This is getting really long, I'm sorry.
It's been 5 months and a half since she left now. I'm 20 years old. I cry almost every ****ing day. I feel very angry at myself for not being able to move on from someone who hurt me that bad. But I love her so much; sounds stupid at my age but I believe she is the girl of my life. I'm living abroad for a few months right now. It's helping a bit, but not as much as i'd want to. I talked to her for the last time about two weeks ago. It went bad. I'm being intrusive because of how desesperate I am and worry a lot about her even tho I don't know why. I'm doing my best not to do this again. I won't talk to her again for now and I'm gonna do my best to respect her life right now, but I just want to make her happy. I know I'm far away from her right now and nothing can happen. But I just can't shake the feeling that we could still have a lifetime of happiness together if we worked hard for it. Probably kind of lying to myself. One thing I'm sure of is I cannot bear the thought of not spending time with her ever again. This fear is probably the hardest thing. I thought we would stay together forever. She's my first and only love and letting that go is though. I dated a girl for a month or two late 2017 but it didn't work out. I broke up with her, telling her the truth : I didn't want her to be a replacement for a girl i couldn't forget.

I'm sorry for this really long post. I've obviously left out a lot of details, but it's the first time I write about this or generally explain so much. My friends helped me quite a bit but I don't want to get depressed in front of them all the time. If I told them everything I would spend almost everyday telling them how shitty I feel.
I don't know what to do. 5 months and a half of being a mess is way too long for it to go away easily i think. I think just waiting more isn't gonna do me well and I've got to change something in my behaviour. I don't know how am I supposed to move on. And I also want to believe I can have some kind of a chance with her in the future, although not for some time probably.
I could really use you guys' help. I'm really tired of being unhappy, usually not being a gloomy / sad person at all. I know I can't get back the happiness I had with her but I'd like to find some sort of closure. Thank you guys. I'll gladly answer anything u might wanna ask.