Are either of the boys neutered or are they both intact? And are they about the same age? I'm pretty new to Gliders, but in some ways they're like most other mammals. Cola may be so sweet partly because he's not getting affection from his cagemate and needs a friend.
I can think of some situations that could push Coke into being abusive. If he is not neutered it could just be that he is seriously dominant and trying to intimidate everybody. He might calm down after being fixed.
Some animals act out when they feel ill, have you had him to the vet to check him out?
Maybe he just doesn't like Cola and got mad when he smelled Cola on you? Can you try separating them for a while to see how they act? Maybe get a temporary cage for one of them? I separated a female with joeys out of a trio because everyone was acting weird and it only took 1-2 days to see a big, positive difference!
If Coke has always been high-maintenance then a previous owner may have lost patience with him and not treated him well. It could have scared him and made him afraid to get close. If you know someone of the opposite sex you could see if they have better luck working with him? Like some dogs/cats really prefer men or women?
Just some ideas for you. It may take all the tips and tricks you find on here and other boards to bring him around. Best of luck, please be sure to update us periodically!