So long he loves and cares about you, helps you taking care of your children emotionally and financially.
Especially when both of you are in the high income category, NOT getting married means tons of money saved in tax! Well, if you want to get married and he doesn't, then don't wait. I persuaded mine NOT to get married. We have been living together for more than 5 years now. Of course we argue and even "fight" like married couples, but we always reconcile afterwards. If you do love him and he loves you. Marriage is NOT that important. That said, everyone is different, if marriage is the number one thing you want, leave and find someone who wants the same!