Wow. I was in your Same situation two years ago. 6 years. No ring. Embarressed, ashamed, jealous of all my friends. It was horrible. One day I woke up, literally out of the blue, called Mr. Wasted Six Years of My Life and said, "Hey, I'm not coming over today. In fact, I'm very unhappy, and it's over." I was estatic for a couple of days, then... well... then I cried for about six months. But I DID get over it. You have to realize sweetheart that he either doesn't want to get married, or doesn't want to marry you. If you meant anything significant to him he would marry you because that's what you want. I know many guys who weren't too interested in getting married but did anyway because they simply wanted to be with their girlfriend for the rest of their life. And if marriage is what she wanted, so be it.
I am with someone else now, it's been a year and a half, and I'm hitting 29 in six months. And I rather die than go for more than two or three years without an engagement ring. I learned the hard way. There is nothing wrong with wanting to get married. In fact, there are many men who want to get married too. Dump your "boyfriend" and find someone who wants the same things in life as you do. It will suck, and hurt like hell, but in the end, it's probably the best thing you ever did for yourself.
Free yourself from marathon relationship prison!