My relationship of thirteen months is damn near perfect. so why am i so worried?

I'm twenty years going on twenty one years old as is my bf (12 days between us exactly) as it says in the title we've been dating for just over a year officially. We met last year at work and there was an instant attraction/connecting. Within two months of meeting we began seeing each other and made things official on the third date after he gave me my first kiss. I had been waiting a long time for someone who I felt connected to and he was it. He tells me often how he's never felt a connection with anyone else like this and i know things about him no one else does. None of his past relationships have lasted so long or gotten as serious (we now live together officially after a good eight to nine months of us unofficially living together since I was there so often) he tells me he's in love with me and wants to get married in the next five years and this sounds great but part of me is terrified that since its going so well for so long now (one year without any real fights and only a few disagreements total. And he's still so loving and affectionate..if anything more than he was at the start!) I can't help but fear its going to all turn to crap soon and I think its because of watching my parents lousy marriage even though we aren't much like them. How do I get over this irrational fear? My poor bf seems so down when I obviously push marriage talk towards getting married later as opposed to sooner. Im just scared.