I'm terrible at relationships, help!

Hi,

Sorry I realised this is gonna be really long but I really need help to understand what went wrong and get some advice. I wrote in 3 parts to try to improve this (?).

1) In my former school (in my home country), in first year, I used to be a total cliché, like I was the chief cheerleader, dating the football team's captain, partying way too much, etc. And then, my grandma committed suicide. We weren't that close but I felt bad, especially as I couldn't go to the funeral which was on the last day of my exams.

So, just after the last exam, I go back to my room and try to call my mom, but my boyfriend starts ringing at the door and won't stop. I open to him, and he comes in like "wooooh it's 4pm and I've vomited 3 times, why won't you go to the party?". He won't leave, so I follow him to the hall's party. There, he leaves me to go with his friends after like 10 minutes, and to be honest I start drinking way too much.

Next thing I remember, I wake up in my bed and get a weird text from a guy, he's like "You were so drunk, I tried to kiss you and you did not even say no immediately". I tell my bf what happened as soon as I know, and he tells me that it's okay. Well, doesn't seem that it was, because he was best friend with the whole rugby team, and as soon as they hear the rumour, half of them decide that no one should talk to me. I used to be their icon, and suddenly they would go to people talking to me and (in front of me) tell them things like "you don't know? we don't talk to her anymore, she's a slut", so it was pretty hard.

My boyfriend stayed with me the whole time, but did not tell his friends to stop at all. Even when the guy I kissed told me that he could go talk to them to tell them the truth, my boyfriend told him not to. Then, two months later, he left me (totally unexpected) because we did not have enough "projects". After the breakup, obviously he totally let his friends blame it on me. Rumour even had it that I was the one who left him.

2) The summer after first year, I was still having sex with him, but also with my "first-year-best-friend-turned-sexfriend" (started like two weeks after the break up, no one ever knew about it). At the end of the summer, I told my ex-boyfriend that I could not see him like that anymore. On the other hand, my ex-best-friend told me that he had feelings and that I had to choose between a serious relationship or nothing. Selfishly, I didn't say anything but he changed his mind and told me that we could still be sexfriends. Still, I knew it would hurt him so I also ended it, and we never talked again after that.

Then comes my totally messed-up second year. First week of school, after 4 parties and 5 guys kissed, I ended up being more interested by one of them, G. We kissed at some more parties but, at the school's first week end (which is at the beach, with everyone drunk the whole time), his friends told me that he had a girlfriend outside of our school so I let go. During the same weekend, lots of guys were flirting with me, and a guy, S, told me that I should date someone to make it stop. As he was pressuring me, I gave him the name of L. Well, turns out that they were flatmates, S told L, and a couple of days later he invited me on a date. We went out on several dates like that, but he finally told me that he was still recovering from a breakup and that he didn't want anything serious. So I decided not to see him anymore.

After that, I dated another guy, but broke up after just 3 months because he was leaving far away for more than 6 months. A week later, at a party, I was still pissed and did totally blackout after binge drinking. As I remembered talking to S, I asked him what happened. I had kissed several guys, including all his flatmates, except himself and L, who wasn't there. After that, I started kissing all of their friends at parties, including L and G, after he broke up with his girl. On the last nights of the year, after seeing L leaving a party with his ex-girlfriend, I even slept with G. On the very last night, he told me that he would have like something serious but that he knew it was impossible as he was leaving for another country. Then, his bestfriend called him totally lost, and he left me to join her. As I was kinda sad, I called S who decided to come to my flat to comfort me, along with one of his flatmates, C.

3) We ended up talking a lot by messages with C during the summer. During the same summer, my first year ex-boyfriend visited me to have sex with me, and I started dating a new guy. The summer over, as I'm doing an exchange in the UK, my new boyfriend followed me there, as well as C and my ex-boyfriend from second year. After discovering that my boyfriend had cheated on me just before moving to the UK, I finally broke up with him. Then, C told me that he had feelings for me and, remembering how I hurt my ex-sexfriend, I asked him if he'd rather not talk to me at all. At first he said no, but ended up saying yes. We haven't talk since then, I just know that he's left the UK. S also does not talk to me anymore, which I don't really know why, but L is the only one of their former flat who I still talk to sometimes. Currently, it's the end of third year, I'm dating a really nice guy and we're moving in together, but I miss talking to C, as he was really my bestfriend until December.

So the questions are: wtf is wrong with me and relationships (inc. friendships apparently)? Can I talk to C again or should I just take on myself? Is it ok to still talk to L?