Hi Paper Fedora
A few things spring to mind, so I'll just post them.
You are 19 and quite successful for your age it seems. But still only 19, all the same, and that is very young. (I have sons in their 20s, by the way.) Some people do meet their life partners by this age ~ I did ~ but not many people do.
However, while many people have not met their life partners by this age, many have already fallen in love ~ and first loves are very very special.
You went out with this girl when you were just teenagers. Such relationships rarely last, as I said, but sometimes, even if they have already ended once, they can be revived. Someone else on this forum is going through something very similar.
Maybe she wants you back.
You say that you still care for her ~ do you want her back?
If so, and she, too, is keen, then give it a go.
You may or may not get hurt again ~ emotions run very high when you are young, but, if you are both willing to try, it might be worth it.
Why are you so miserable, if you care for her and she is back in your life?
Have a think.
What do you actually want to do?
Good luck
