At 15, she may have feelings, but she is far too young to be involved in a serious long-term relationship.
As I said before, 16 is very, very young ~ and, obviously, 15 is even younger. I'm not even sure that I think 15 is even old enough to date seriously, never mind to decide, or know, if you have met 'the one'.
I didn't meet my husband until I was 18 ~ and even that is very young to start going out with the person who will be your life partner.
You have changed a lot in the last few years, I'm sure, and you will go on changing ~ as will she. Teens are transition years ~ the best of times & the worst of times.
To talk of spending the rest of your lives together, getting married & having a family, at such a young age isn't a good idea ~ or even realistic.
Enjoy your youth & get to know different people ~ boys & girls ~ but don't get too serious or make long-term plans just yet.
Emotions run high during your teens. She may come back to you; she may not. You WILL get over it. This happens to lots & lots of people. Maybe if you talk to her you will get some sense from her or maybe you will meet someone else soon.
Don't give up on finding 'the one', but don't, at 16, expect to find the girl you will marry. You might, but you are more likely to meet her ~ or meet up again ~ when you are old enough to be in a settled long-term relationship.
Maybe that was what your girlfriend couldn't cope well with. A lot of people might find it a bit frightening to make future plans, like that, at 15.
Take care.
