It's wrong that we 'know' who the right person is from comparing experience to others. I don't know many people who would say that. Logically, yes, first loves will not last but this is more likely because people will have them when they're a bit younger, and will grow up struggling to keep things together as they mature. Which is nobody's fault at all. It sounds a little like this could be happening with you. I wouldn't be worried about it being your 'first love' and that's why it shouldn't be the right one, I would be worried because after a year, and with her being 'madly in love with you', you still only 'think' that you love her and say that you 'care' for her before the love. That's a red flag to me.
I'm with my first love and I'm pretty sure, as much as I can be, that he is the 'right' one, and we have had huge issues. But I don't think you're supposed to know, either, and certainly not after a year. The fact that you want to know something like this so much is another red flag; there are worries and then there's making a thread for your fears, and the latter does suggest a bit more than a simple 'curiosity'.
I think you should have a big think about what you want, about whether you want to continue this at university or whether these thoughts are becoming an excuse for you to think negatively about the future for you both. Work out what it is you have an issue with a little more specifically, and then communicate with your girlfriend so that there's no confusion, and that she has a chance to respond to these questions herself before you take any 'rash' choices alone.