Hm... you're 23, it's been 8 years. Doing the math, that puts you together at the ripe age of 15 for you.
Now that you're "single," you're feeling the life of an individual, and realizing on some level that you have never been alone, never developed yourself as an individual, or as an adult. I suspect you feel he's the only one for you because he's all you've ever known. How on earth would you ever know if he's "the one" if you have no other experience?
I found that the only way to free myself of all tlhe crazies that I thought were brought about by things in relationships that "if only" would happen is to take a break from obsessing on the relationship and find out what it was inside me or lacking inside me that made me feel the need to obsess. And for me, the only way to do this work was outside the noise of a relationship, particularly a relationship with an addict with arrested development and lack of life coping skills other than substances and manipulation of enablers.
It hurts, to be in that scary place where you are all that's left, and you have no idea who you are; I remember it.
Good job for reaching out and looking around for answers! Keep looking, and don't be afraid to try new and different things! You might just stumble across something waaaaaaaaaaay better!
CLMI