I originally housed my rescues together because they had always been together and I was worried if I separated them I would have problems. My female used to do the same exact thing, killing it and rubbing her nose all over the prey but leaving it because she was insecure about the other snake. I got them to eat but I would have to take one snake out to feed the other, so I eventually gave up and moved them both to tubs. So that would be my advice. Even though she was previously housed with another snake he might just be insecure because it's a new environment and because he doesn't really "know" the new housemate. Buy a tub, get him eating regularly and then decide if you want to introduce them again (I don't recommend this).