He's likely lonely -- sugar gliders are social animals that should be kept in pairs. When they come into our rescue they often spend a few weeks like that if they've been separated from their friend (people will often abandon half of a pair if one is "unfriendly"). They're usually super glad to be introduced to someone new.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry