Dear Alice,
this is my first time visiting the site and read all the posts above; wonderful advice and I am sure I can benefit from those advice and videos as well. I will watch those videos later to learn from them as well. I am going to attempt to help u on this.
1. you are very young, as belove hinted, and u have a lot ahead of you. thou it may not seem like it at the moment
2. try to think outside the box. try not to think of this but think of something else that is similar; compare this with decision making. we make decisions everyday, every moment; when we have a difficult decision, it means the two items have a similar VALUE. think of it, if u like X more than Y, then naturally the decision is quick and easy. X is your choice but when X and Y are similar in value, the decision is harder. think of u going shopping and can only buy 1 item out of the 2.

this decision can be difficult, some people will ignore it and let it be by not doing anything. Deer in headlights syndrome. Some will get stressed out and it leads to anger, frustration, and ultimately more suffering. or u can think outside the box and look at the problem objectively.

you need to know you have a situation
you need to know that you are in a difficult state that is causing you to be unable to function at your optimum state
you need to let go and move forward.

the hardest part is letting go and move forward but that is thinking outside the box. let go of what is expected of u, let go of what u believe to be the best thing in the world at that moment. If you believe this person is the most perfect person in the world. in your mind, u will have regrets and guilt cuz how can “I” let her go. But there are 7 billion people in this world. Let go and open your mind, u are still young and the world is a very big place. as you move on, u will grow and your opinions will change. u will meet other people. The best thing for now is to have fun; do something you enjoy, join a group, or create a gaming group. When you think of her or something reminds u of her, know that u are having those thoughts. eventually, it will go away but for now, enjoy life; enjoy your youth. have a joyful life because u have a choice.

I wish you happiness and I sincerely hope this is useful. May you be happy! May we all be happy!