It sounds like your brain is on auto pilot when it comes to thoughts of her. This is what I would try. Every single time you find yourself thinking of her say STOP! Say it in your head or say it out loud. Every time. Within a few days you should find yourself thinking of her less. This would be a really good time to take up a new passion, you need something that makes your soul feel good, something to fill the spot thoughts of her have dominated.
Firsts are the hardest to get past because we are so innocent and unguarded. And when you are the type that let's few people into your inner self, it's even harder. If you decide to date, maybe try dating a variety of women with no expectation of it ever being serious, just to get yourself out of your head a bit.