How do I keep my girl friend from leaving me?

We started dating March 7th this year. 2 weeks into the relationship she told me she loved me while we were laying in bed together, sober and non-ually, sleeping together. A dew days after that marriage became a topic and she said she could see her self marrying me, I brought it up though. Her father is in Delaware for military training until July so it's only her and her brother. I stayed at her house for nearly 2 weeks like we were married. We do have but it's a "making love" , not just a spur of the moment . Anyway, she hated it when I had to go to work or even when I went to the other room without her. I loved that attention so I fed on that became the same. This past week she said we need time apart bc we started bickering, understandable though. So we are having a few days til the end of this weekend with no hanging out. I've become jealous of every person that gets to see her. I've never been a jealous boyfriend so idk how to handle this. We are both 20, almost 21. Today she told me she was going to hang out with her friend, Myles, of many years. It's completely plutonic but I was angry that she wanted to hang out with another guy, her best friend, n not me. We argued about it I was wrong to be that way. She now says that she's unsure if she wants this relationship bc we fussed n fought this whole past week. Please help me, someone. I love her with all my heart even only a month n days after but I can't lose her. Help me please.