Why Am I afraid to enjoy and take my happiness(LOVE)....?

I think I have this barrier, I find it too perfect and at the same time I think, IT's TOO EARLY to COMMIT for a lifetime but there's nothing else I would like? It's like a dooms thought to be with someone till the rest of your life, it's tottally killing me, I think I'll seperate with her because of that enormously strong inside eating FEAR!!!! I'm 23 she also. I'm so CONFUSEDDDDDDD and the happiness is so big that I couldn't imagine my life with somebody else, I HATE IT, I FEAR IT, HELP please, advise mee :(:(:( My whole god damn LIFE, is this how we are created?!?!?! IS IT??!?! TO BE MONOGAMOUS!!!! IS IT!?! damn it am nervous...