I have two friends, both good people, who amicably agreed to their ex-husbands having custody after the divorce. In one case it was because the mother was relocating and wanted the child to stay in the better school district and in familiar surroundings. In the other case it was because the mother honestly admitted that although she loved her children her husband was just more suited to be the primary parent (which wasn't a surprise to anyone...he'd always been the one to do late night feedings, call in to work when one of them was sick, do "kid duty" at get-togethers, show off the latest pictures, etc.)

Good luck working it out!