I really don't want this to be or to sound patronising, however, here goes: Why didn't you try to marry him first, THEN start the family?
At least then you may have found out his "true" feelings for you. As it stands, it sounds like he's having his cake and eating it, if you'll excuse the expression.
The reason I'm saying what I am is because you sound as if you're not only doubting his commitment, but perhaps you're also wondering whether to "bin" him, which of course would have been a damned sight easier without the added "baggage" of having little ones to consider?
Personally I don't think you're wrong at all for wanting marriage but maybe I'm old fashioned - it seems that the "norm" nowadays is to co-exist as you and the boyfriend have been doing.
However, the commitment of marriage cannot be one-sided, therefore, you need to ultimately decide what's best for you, and your children.