Your putting a lot of pressure on yourself for things you "didn't" do. I used to be one who spent every day all day with my gliders ( I am not saying this to brag or make you feel bad there is a point ) Which was easy, I don't work, or have kids at home, or leave the house for much of anything I'm pretty much a hermit so I have lots of time to spend with them. With one it was easy, with two it was no different, with 4 I had to do two shifts, now I'm up to 7 with an 8th coming in a few weeks.
I currently have 3 cages, a trio in one cage a trio in another and single guy in another waiting for his cage mate. My life has gotten a little busier though I'm still home all the time I just don't have as much time. My gliders are fine, they still get attention just not as much and ya know what they don't need it as much, they have each other. Do I feel guilty, sure sometimes, but they are far from neglected.
The trios are "bonded" to me however, the single guy is a work in progress. I don't take him out nearly as much as I did the others. Not because I don't have time, but because I am more active now, and if I have chores to do he gets stressed over to much movement. He was also shipped to me, he was a very sweet baby with his Gramma, but for me is still crabby and pouch protective but getting better everyday. Still super sweet, just very vocal lol He is young and intact and very full of himself. I know I have some work to do with him as well before his cage mate arrives, which also may mellow him out. AS I was typing this I just got him out of the cage since I'm still sippin coffee n not active yet, he got treats, nails clipped and into the bonding with a little loving in between...
My point is, it is ok. Don't stress over what you didn't do before and focus on where your at today and where you would like to see your relationship at with the glider tomorrow. Gliders are adaptable and very forgiving, the "bonding" only means your building a relationship with him and relationships grow over time, they don't stop growing. Your paying attention to his behavior, your getting to know his personality just as he is getting to know yours. I could give you a few bonding tips and pointers but I think your already doing what you should be doing. It takes a little time just try not to have expectations of him or yourself and where you "should" be You are where should be, and it will continue to progress. Every glider relationship is different I can't compare one glider to the others, they may be a colony but they are still individuals too.
Relax, and enjoy your glider... if you have depression he will be an excellent companion for you ps I take naps everyday, and there is always a glider in a bonding bag on my head takin a nap with me. You can "bond" with them while you both sleep.
I'm not one to preach about single gliders neeeeding a cage mate, so I won't to you either. But I will ask this
how big is his cage?
does he have a glider safe wheel?
does he have stimulating toys in the cage?
The answers to those questions may have something to do with his "freak out" in the cage behavior