Am I crazy? 🙁

Is it still crazy to believe that someone's "first" can be their "only"? 
I'm 19, been with my BF for going on three years now and lost my v card to him this past September. We both are crazy about one another and want to get married a year or so out of college (yes I'm a romantic but the wish to marry is mutual on both ends). But so many people have been discouraging me lately saying that I didn't explore any other options, or I put all my eggs in one basket, or that I'm just "obsessed" with him. It's quite upsetting to hear given that when I look to my future I can't picture anyone else taking his place. I just hate it when people make me feel bad for loving and wanting to be with him 🙁