Are me and my boyfriend meant to be together?

Me and my boyfriend were like middle school sweethearts. We went out in the seventh and eighth grade and he had been my best friend since I was 2 (I'm 25 now). After 8th grade, his family moved to Korea (job related purposes) and we lost touch after a few months. I missed him so much, I mean he meant so much to me. He was my first everything and it killed me when he went away. When I was a junior he moved back into town. I was happy to hang out with him again. He wanted to get back together, but I had been in a one and a half year relationship at the time. I kind of avoided him at first, but my feelings for him were too strong so I broke up with my boyfriend for him, but we went our separate ways after graduation (the colleges we went to were literally on the opposite sides of the country and we didn't think the long distance thing would work) and we kept in contact for a while. I ran into him when I was 22 and that point I was in another serious relationship. We innocently hung out as friends for a couple months, but once again he pursued me, but this time I told him I was not going to break another guy's heart for him. We had a huge fight and after that we stopped talking. My boyfriend at that time proposed to me after that, but I said no because I knew I still loved my ex and it would have been unfair to marry him knowing I was in love with someone else, so that relationship ended. I recently moved to another city and a met up with him again on Facebook. Its like no matter who I'm with, I'm always secretly thinking about him, so I thought why not? (At least this time I was single). Now we've been together 2 and half months and he proposed to me a few hours ago. Don't get me wrong, I love him with all my heart, but I feel as though maybe things are happening too fast. I mean, I know I want to marry him, have his babies, grow old with him, but I'm not sure if I'm ready to do that now. I don't want to say no, because I don't want to lose him, but I don't want to say yes without being 100% sure either. Does what everything that's happened between us in the past mean that we're meant to be? You know, like fate or something?