I'm afraid I'm going to ruin everything

I don't know if I'm in the right place to post this so I'm sorry if it's the wrong section. Here it goes:

I met a girl and she was wonderful, but with time I ruined it because I'm paranoid and I always think something's wrong and keep asking "what did I do?", even if she keeps on saying I didn't do anything. While I was feeling miserable with this girl another friend kept cheering me up and helping me with everything, and now I have some kind of relationship with her but it's all happening again.

Recently we've been fighting all day, and I blame it all on me, I have an irrational fear of losing her and losing everything because of... Well, me. Because of the way I am, I feel like she doesn't care as much or doesn't love me as much and one day she'll get tired of everything and just leave me, so I want to change, I really want to change because she's the most important thing in my life right now.

I'm the kind of person who will just... Suffer and go through anything as long as I don't lose her, it doesn't matter how much I will hurt myself. But I know it's not the case with her, I know she will dump me once it gets to a certain level. I don't want her to be upset with me and I'm willing to do anything to keep her happy and to not bother her, the thing is I can't help but feel this fear of ruining everything, of losing her because of the way I am.

I'm going to travel in 1 month to Europe, for seven months and I will be seven months away from her, and we don't see each other much to be honest, so I always try to go out with her, but everytime I ask her out she says "I don't know", that upsets me and she says "it's the way I am", and she won't even try to change a little bit. Seven months. I really want to see her as much as possible but she keeps saying "I don't know", then I get angry and we argue and I end up regretting everything and apologizing and the fear of losing everything comes back to me.

Another thing is that she doesn't communicate with me much, she won't tell me what she's doing or where she's at or what she did the whole day, it's always "things", "somewhere", "stuff" or "nothing" and that really bothers me because I like to know what she's up to, I care about her. So we argue, i calm down and start apologizing again, only to be afraid that she will leave me and it will be my fault.

I wanna change and I don't know how to do it, please, I need help. I know she won't ever change for me and I know one should not change for anyone but that's not how it works for me, id do anything as long as I don't lose her.