Wow, you are in the EXACT situation my aunt was in about 4 years ago. She had been married and divorced as had the guy she had been dating for SEVEN years. She always wanted to marry him, and they really were in love (it seemed to me). They actually lived together for a while, and the whole time she kept trying to get the strength up to say "marry me or I leave". A few times, she moved out from him just to say, "I'm not moving back until you agree to marriage." It was something important to her as well. (And she has never been a JW or overly involved in church, etc.) So this went on, and toward the end, they were on again/off again for about a year. She finally got counseling and got some self-esteem. She realized this is just something so important to her, and by him not agreeing to help her reach this life goal, then he just really didn't love her to the extent that she needed from him. they were both sad, but she finally broke it off. She moved back in with Grandma and Grandpa, got a second bachelor's degree, changed careers, and is much happier. She took another class to learn a new language, met a nice, funny, and respectful-to-her-wishes guy, and they got married! She's been married for about a year or two, and she seems really content. She used to be always sort of on edge and quiet, but I would say now she overall seems more hopeful and content/calm.
So that's one way the scenario could play out for you. I disagree with most of the above posters and I say you should leave if he cannot respect you enough to swallow his fears and marry you. No, marriage is not that different than dating (it's like you go to his house, but you never go home!) and you do have that "prestige" in the family and among friends that you can't describe unless you've been married, but if it's something you want, he should do it for you. You've waited long enough.
By the way, I think my aunt regrets staying with that non-marrying boyfriend for so long. She always says in the end he didn't respect her wishes enough, and she put up with it for too long. She's now about late 40's, so she's like 10 years older than you. You're not that old.