Definitely don't keep them together. If you haven't had a parasite test done yet, now is the time (and if he comes up positive--you will have to treat both snakes).

As for his behavior...perhaps he's feeling better now. He may simply be a flightier and more nervous snake than your other one, and it will take time to tame him. He probably wasn't handled much in his previous home. When an animal is feeling poorly, it will put up less resistance, so his new behavior may just mean you have rehabilitated him successfully.