If you haven't found an answer to this yet--
He definitely needs a balanced diet. Try to get him on HPW (CritterLove) or BML. These are commonly recommended in this forum. It could definitely be food causing hair loss, but I recommend a trip to the vets to see if he has anything else -- parasites can cause hair loss too, so be sure to do two or three fecal exams (some exams will be negative even if there's parasites, so multiple exams are needed).
I have a single glider but he's been single all his life with no problems. He bonded with me in 6-7 months and all I did was keep him in his pouch a lot, pet him a lot, talk to him keep my hand in the pouch while he slept, and hand fed him. He doesn't like toys so I never did out of cage play time. He's food motivated so hand feeding him helped a lot.
That being said, a second glider absolutely helps and is usually better than a lone glider. Some gliders need a buddy, some don't, but they're always happier with a friend.