Is my relationship anxiety normal or is it the cause of my disorder?

My boyfriend is 25 and I am 18. We've been together for seven months. I know this doesn't seem like a long time... no, rephrase. I know this ISN'T a long time to be together, but my relationship problems go beyond your typical ones. I am autistic. It's nothing dramatic, it's called Asberger's Syndrome and it's probably the most mild form of autism. However, it affects how my mind deals with relationships and people, including my current relationship with my sweetheart. Before him I hadn't had a relationship over three months. He was pretty much the same as me except for he had one relationship that lasted eight months. I live with a wacky family whose constant pushing and prodding about children and marriage drive me to the brink of my sanity. It's a miracle he's been able to deal with and even embrace them for the last few months. However, I can't help but long for him to propose and it's driving me insane. I think, however, my problem lies in my troubles developing and maintaining a functional relationship and my psychological countdown and dread to OUR eight-month anniversary. It seems to be steering me towards a desperation to get married. I know the obvious answer is WAIT until we've been together long enough to seriously consider marriage and even wait until I've received at least my BA, but my nervousa is constantly breaking me down and making me wonder if the minor problems we face in our relationship could escalate into the fiasco that destroyed his last eight-month relationship. I know I should trust that he loves me enough to talk to me if something was wrong, but my supply of faith has been exhausted. I feel as though in a marathon and I am ready to give up because of some sort of genetic defect. We both love each other very much and for the first time it's not the juvenile swept-off-my-feet “in” love feeling. It's steady and... mature-feeling. It's the feeling of being happy because he succeeds or knowing what to do brighten his day. His simply being there changes my entire day. We have both caused hurt and pain for the other, but are somehow still together and I enjoy our time together. We never actually have to do something to have fun. It's just us. I just wish I could be more laid back and not worry about eight-month markers, marriage, or kids. Is this normal? Am I simply experiencing female paranoia and anxiety or is my autism flaring up and dooming me to a life alone or worse... divorced? And how in the hell did so many married women wait numerous years before getting married?