Hi, I'm new here and I don't really know how to start...

So me (22M) and my girlfriend (20F) have been together for 5 years. I'm studing in the city about 60 kilometers far from her city, but I'm coming back every weekend to meet with her, since I begin my studies. Everything was fine until the last summer when she decided, just like that, to tell me that she want to try to be with other man, because our relationship is boring. My heart just stop beating, after a long discussion I convince her to stay and I've never told anybody about that. Then she met with her ex (twice, first time during concert second time in his house for a party), maybe it seems like I was jealous, but it really was sus for me, especially after what she said to me. She was chatting with him and I didn't want to restrict her. She told me that he asked her for nudes or a kiss, she claims that "it just a joke" or "he was drunk", I was angry af. Fortunately she stopped chatting with him. It was a year ago, but I'm still thinking about what she said to me and about that sick situation...

I'm not a party guy, but sometimes I want to go with my friends (females and males) on a beer, she was mad at me ever single time I was doing that, talking with her do not help and I decided to avoid meetings (covid helps me a little with this). Now I only have her, and even though I feel very lonely.

Recently she is acting really weird, like she was mad at me all the time. She starts to chat with younger guy I do not know (and she is saying that he is cool etc.), she is complaining that I don't have enough time for her (I feel like she do not understand that I want to pass my exams. Of course we've talked about it, but she claims that "studies are more important for me").

I don't know what to do in this situation. I start feeling like she is not a girl that I love anymore, that she is becoming a stranger to me. I'm scared of loneliness and I feel that if we break up, I will be alone with everything, with no friends. Sometimes I think it is the only way to solve this, because conversations don't work, but it is hard as hell after 5 years, so many memories...

Sory for "crying" in here, but I'm broken. Sory for my english too, I'm still learning.