6 years and still no proposal

So when i met my current boyfriend I had just finalized my divorce. I married a man who was more committed to various other women so I said goodbye to that nightmare and moved on. I told my boyfriend when we met that he had 5 years before I would start wanting to discuss marriage. Well, year one was perfect, year two, he got me a gorgeous $1500 promise ring. Year three, we moved in together. We have fights from time to time...normal stuff. So last year was 5 years. I didn’t bring up anything about getting married because I want to be surprised. Well, nothing... and we just hit 6 years this month. About a month ago I had a freak out moment on him when I heard his friend was engaged after being with his girl of 2.5 years. And all of our friends have gotten married, engaged or had 1-2 children faster than we moved in together. After my freak out moment I’m feeling discouraged, like it’s never going to happen for me. Has anyone gone though long relationships that take forever to get to marriage? If so, how do get over the bitterness? And how do I help my BF get over his fear of marriage? We have discussed babies before and he is on board with having one within the next few years. But, he has this fear of marriage because he comes from a broken family.