Sorry man. Despite all the time you spent together and the closeness you felt, she was ultimately not the girl for you. People change.
It'll take time to get over her but you can shorten that time significantly by cutting off contact and erasing all photos, texts and mementos of her. Save photos on a USB drive and lock it away if you like, but don't look at them again for at least a year. Just leave absolutely no trace, and don't leave any workarounds. You don't want to have say an 'important' text catching your eye and retriggering intense feelings for her while she's away lezzing it up.
...and how to stay positive