My twins coslept with us nightly until they were 8 and a year later are regular visitors in the family bed. At 5, both were still nursing & that bedtime nursing was the most critical, so I was almost always on bedtime duty. Although in general I loved that time with them, it does get frustrating to have to be the parent on duty for bed every single night.
We didn't actively do anything to change it (honestly seemed more trouble than coping w/ the periodic frustration), but they gradually outgrew the need. They actually stopped needing me to fall asleep before they weaned completely, so it was't just nursing. I worked one evening a week so DH would go to bed with them that night & they got used to that being part of the routine. As you've noticed, if Mom's not in the house, they can usually fall asleep without Mom! And we gradually got to the point where DH would go to bed with them (they read novels together at bedtime, so that was their reading time) and I would stay up to get stuff done or play on the computer or whatever, and they started more and more often to be asleep before I got to bed.
If you want to actively try to change things, could DH plan a special activity for just the two of them like reading big kid books? There are great novels that a 5 year old can enjoy & understand, but couldn't read on his own yet. If it was their time, instead of DH being the consolation prize to having Mommy, your DS might be more accepting. Or you might plan to be out of the house at bedtime for an extended period of time (maybe take a class or something) so DH putting him to bed becomes routine.
But if you do nothing, he will eventually stop needing you to fall asleep! Actually, up until DS and DD1 moved into their own rooms, we all went to bed at the same time, so they had an adult (usually me) with them to fall asleep almost every night until they were 8. The big change for us was independent reading - when they were able to read well enough and be excited enough about it to WANT to read to sleep, they were happy to go to bed without an adult and take a book and flashlight along instead!