he proposed..?

I'm a teen mom and he is 5 years older than me (no negative comments please) and I'm pregnant with his baby. I love him with all my heart and I understand where he is coming from, but I've already made a commitment to this baby.. And I don't feel like I'm ready to make another big commitment like that. And we are both young, so who's to say we won't change our mind down the road? He's a great boyfriend and will be a great father, I'm just not ready. Advice?