I've always pictured him in my head with Elaine. But that would be tragic, too, because if the Elaine=Kumori and Cowl=Justin theory is correct...
Honestly, I don't see him happily ever after. Not everybody finds somebody. Just look around people you know. Friends, colleagues, neighbours, ... Some people never find the partner for life. For different reasons, and they are all different people. Some people found their partner and lost him/her again. Some love without being loved back.