Multitudes of confusing feelings flying through my head

The title pretty much sums up the situation. I've been having a lot of confusing feelings lately. They mainly center on the bf. In a lot of ways I'm scared to death of marrying him. We haven't been together very long still, and who's to say he won't get tired of me down the line and leave me? That's not so much about me having a lack of faith in our relationship, but rather a lack of faith in any relationship. Who in his right mind would ever want to spend his whole life with me? On the other hand, I want to marry him so badly it hurts sometimes. I am so happy that I never want to let him go. It's all very confusing, and I don't know exactly how it's going to pan out. I don't want my cynicism and fear to make me miss out on what could be my one chance at true happiness.