Marriage....?

I have been together with my guy for almost 9 years,living together for 8. We have three children together but,we aren't married.I used to ask him why and he'd say he wants to have a big wedding typical bull crap answer,but now it has been nine years!I am in no way silly and thinking he's going to marry me one day,I don't think I even wnat to marry him anymore.I'd just like to know why he won't? we share everything else bank accounts,home all that but why dosen't he want to get married??is it because he thinks something better is going to come along?or he still wants to play the field??Thanks.