What's Wrong With Me? No More Sex Drive

I live with my fiance. I'm 20, and hes 25.

For the past year my libido has been on a mega-downhill slope. At first it was just me saying away from the frequency of sex, and then asking my boyfriend to skip the foreplay, and now sex is just sitting like a dust bunny at the bottom of my chores list. He asks and even when I do finally tell him yes...it's because I feel guilty for pushing him away all the time. I just don't want sex anymore. I don't even want him to touch me.

I'm not sure what's happening or what's wrong with me...but I'm afraid of what will eventually come of the relationship.

Any ideas?