<human>: Can you give me the gist of the text in a nutshell?

We've been together romantically for about 5 years. I proposed to her on a whim a few months ago, but I've been thinking recently that maybe this wasn't the best choice for me. She's graduated and in grad school, and I'm still working on my degrees. We're so different in so many ways and it causes problems from time to time, but for the most part we're happy. I have no clue how to even bring this subject up without breaking her heart. She sees me as all there is to life. I'm flattered by this, but at the same time, I think it's probably not the healthiest way to view anyone. Can I get some advice on how to handle this situation? I'm terrified I'll ruin something good, but at the same time I don't want to make a mistake.

The reason I think it may be a mistake is that I have known another girl for about 8 years. Throughout this time, we've ranged from anywhere between acquaintances to lovers. I am interested in pursuing something with her. However, she lives a state away from me now, even though we both still have very strong feelings for each other. What should I do?
<bot>: I may not be in love with the girl I proposed to anymore. How do I bring this up/break it off without crushing her emotionally?