Why do i want to get married?

I have been in a relationship with my partner for 12 years, we have 3 children together and surely that should be enough, yet i long for us to marry. I don't really know why or worried that i am old fashioned and unrealistic. I love him so much and he has asked me a few times over the years, yet he never intended to go through with it.

It seems to plague me now and i just feel so confused. I want us to grow old together but i wish he was happy to make that step with me.

Any ideas??
Thanks
honey