Overwhelmed, advice welcome!

So I am 11w3d with my first child.  Here's the catch,  my
Fiancé already has two children which I love unconditionally and am a full time mommy to them. (Their mother is no where in the picture). All of this pregnancy is so exciting and new to me and I feel like he could care less.  I understand he's been through it but we're completing our family with this bundle of joy,  how do I get him to be more involved.  I just want to give up sometimes!  It's so frustrating and overwhelming!