Why is my fiance so insecure and paranoid?

I love my fiance more then anything and were due to be married in a little over a month. So needless to say things have seriously started to pick up and get stressful well anyways my fiance is extremely insecure and paranoid that i am going to up and leave him at the alter for some reason and he is just getting antsy. Were both 26 years old been together two years so i suppose he could of gotten hurt by another women but if its so he hasn't told me about it. He has just lost all confidence lately as were getting closer and closer to our wedding date and i don't know why and its frustrating me as i love the man dearly but i tried sitting him down and trying to find out WTF is going on with him and he just said "Nothing" and that he doesn't know what i am talking about well i am so close to just postponing the wedding till he gets his head back onto a swivel per-say but i am scared that will just intensify his fears so i feel so caught between a rock and a hard place.