Sorry friends this may be longer than what you normally see and I seek your advice, compared to friends since I know you are unbiased in the situation.

I have been dating a guy since high school for over 10 years. 6 years ago he cheated on me and I moved out of the house (we both own together). After months of not speaking at all, I knew that we would have to meet and settle the loose ends so finish it once and for all. A few days after receiving his text, I found him broken, skinny, and only a shell. I had found out from friends & family after the fact that he was absolutely devisted. He had become a recluse, shattered and he said he made the biggest mistake of his life.
During this breakup time, I made sure not to find out what his new single life was like and I was in the mindset that he didn't care for me and I would keep on and enjoy my life as single.
After we settled our remaining ties, I went to leave and he lost it. For the first time, he cried and expressed his emotions that he loved me and didn't want me to leave without him. And as you expect, we re-kindled our relationship, slowly and now its been 6 years without a proposal.
Here is where we are at today. I have brought up marriage before and he clams up. I am 30 and he has not proposed. I am not in it for a big fancy wedding/party and the bill that comes with it. But a simple close family and friends ceremony to vow our love together.
But why won't he talk about it?. We have an awesome relationship together. He is the perfect guy for me who is kind, caring, still makes me giggle, will help out anyone who asks, and awesome with kids. We absolutely enjoy doing our hobbies together and going away, just the 2 of us. We are rarely apart and rarely even fight, and most fights last a few hours and I cave in because he knows how to make me laugh and take my defense down.
But when I bring up marriage and starting a family together he looks like a deer in headlights. I am now to the point where I am becoming bitter and resentlful with him and can't figure out why he doesn't want to marry me. My friends and family have commented that we are the happiest 2 they know and that he is always trying to make me happy. Not trying to toot my own horn, but I am attractive, have a great job and a bubbly personality.
I know from his past that he has not had great role models for relationship building. Divorce is common in his family and the men are disconnected. Also, his friends love me but they make comments to him that once you get married everything changes.
I am now to the point of the next stage in my life and I am scared that I will always be his girlfriend. I don't want anything to change in our relationship, but I feel that ultimate commitment will soothe my anxietys and low self esteem. I feel I am at the tipping point of either always being the girlfriend or I need to walk away.
Do you have any advice on what my next move should be.

There really isn't much you CAN do. I know that's not what you want to hear, but the issue may not have anything to do with you.
He probably doesn't want the marriage-and-kids-life but doesn't want to lose you by saying so.
Have you tried couples therapy to pick out the root cause? Perhaps he needs to speak with someone not involved in the situation...

You need to walk away because your in an awsome relationship and are just a girlfriend? (at the moment) Marriage is a piece of paper and a ceremony. 90% of the time people are less happy after marriage. I must know 300 married couples I can name maybe 2 that are even happy. I do know 3 couples that have been engaged for 10+ years. They are the happiest people I've ever met all 3. So statistics show marriage ruins relationships. His family shows marriage ruins relationships. His friends say marriage ruins relationships. BUT YET your still wondering why he doesn't purpose... What a mystery

Because you live with him, sleep with him and he has no commitment, you have a harder time if you break up even getting him out of the house, No divorce terms, no spouse support.

So why not you just tell him, set a date, tell him to get in the car to go get a marriage license, he will either do it, or when he refuses you know he will most lkely never.
He has nothing to gain from the marriage.