how do you know he isn't giving his all, people don't live in each others pockets, there's a big world out there, other things to do, that doesn't mean one partner loves the other less for doing other things.
Bob Dylan probably said it best, a little snippet:
You say you're looking for someone who will promise never to part
Someone to close his eyes for you, someone to close his heart
Someone who will die for you and more
But it ain't me, Babe,
No, no, no, it ain't me, Babe,
It ain't me you're looking for, Babe.