My honest opinion is to treat this like an adult.
Value your circumstances. Sure, there are friends there and you know the place, and you have relationships, however you can make friends at a nightclub, can't you? However I do not think that a nightclub would be best for bettering your education. School would be best for bettering your education.
Similarly, you need to decide. Are you at the barn to make friends, or are you seriously there to better your riding? If if it is your desire to learn how to jump, it would be for your own benefit. If it truly hurts you, thank your trainer for all that you have learned, and perhaps offer to do some volunteering if you wish. You can keep your old friends if you stay in touch, but you as well will make some new friends as well.
You sound like an average riding child to me. You grow up a little girl that rides simply for the pleasure of enjoying it, but as you grow up you are learning what you want to get out of riding, and learning similarly that you are not accomplishing such tasks at the barn you are at. I had a similar incident--I rode for the joy of being with horses and engaging with them, however I soon learned that I was not accomplishing my money's, time's, or effort's worth at the barn that I was riding at. Because you have taken notice of this, I would take this opportunity to grab life by the horns and go for it!