I’m sorry you are in such pain. And I’m very sorry that you aren’t going to like my advice. You met this guy online when you were at the very impressionable age of 13. The two of you had a wonderful fantasy about love and relationships that simply won’t hold up as young adults. Although you have powerful feelings for him, they aren’t the feelings of mature love. He can’t be “yours.” People who love each other don’t own each other. You two broke up 3 years ago. He has grown beyond the fantasy and you haven’t. Unfortunately, staying in contact has only helped keep the fantasy going on your part.
My guess is that you are afraid of having a real life relationship with a person who is truly available to you. You cover those anxieties with your obsession about a boy you’ve never met. Both wanting a relationship and being scared of what it means is a normal part of the teen years. The way past the fear is to be friendly with guys you like and to start going out in a group to fun activities.
If you can’t do that, I do suggest you consider some therapy at this point. Three years is a long time to mourn the break up of any relationship. In your case, it is preventing you from experiencing an important period of personal growth and development. You can and will find real love. But only if you make yourself available for it.
I wish you well.