First loves are hard ones to lose but time will eventually heal old wounds, i do not believe in time travel those who say they have give 0 proof to there claims its a fad brought to life by Back to the Future. The only thing you can do is suck up what you have left and move on, dating isn't something i would look into at your age to many kids dating kids and it ending badly worry about life in the moment and your future and in time if someone was meant to be in your life they will find there way.
You will gain and lose people all the time through your life those meant to stay will, perhaps it doesn't work out with her friend and a few years later you 2 make it back together, you don't know or maybe she does come back to you and your in a relationship and happy and don't want her back. Living in the past and wanting for the past isn't the way to live you will drive your self insane wishing to change the past. I am pretty sure all of us wishes we could change the past and as you get older you will realize it will be for something else besides a girl. Hell i wish i could go back and kick my self in the face for taking so long to go to school and screwing off with my friends and chasing girls instead of studying and graduating high school and going to MTI like i could have.
Do i regret it? yes of course, do i wish i could change it? again yeso f course. But i don't dwell on it and spend my time wishing it was different the past is the past and despite popular beliefe it cant be changed, you have to move on and continue on with your life, there no shame in missing her.