<human>: Can you provide a brief overview of the text?

Hi r/relationships, I'm new here. A quick background: I am a 19M that has been dating a 19F nursing student for nearly a year now. She is my first everything, and I am her first LTR. This girl is utterly amazing, she is kind, trusting, intelligent and beautiful.

 I want to write her a love letter as part of our one year celebration, and hopefully every year after that as she's never had anything like that done for her before, and she's given me the impression she likes that corny love stuff like that. Also we have talked many times about living together, our future together and whatnot. 

The thing is, since I'm her first real boyfriend, I don't want to scare her or make her suddenly feel trapped and push her away as ive read sometimes happens. My biggest fear is she'll decide she wants to see what else is out there or wants to see what other relationships are like. Any advice on what to put or not put in my letter? I want to express just how important she is to me.
<bot>: a young man who loves his long term girlfriend with all his heart wants to write a love letter for a one year thing, but doesn't want to make her suddenly feel trapped. What does he write?