Hi there, first time using this sort of website so please forgive me if this is in the wrong section or there are any errors!

I've owned my three gliders for 8 years. Two sisters and a castrated male. They've got on throughout the years, but the male (who was introduced a year after I got the girls, so he's a year younger) has always been antisocial and timid. Where the girls were always friendly and no issues, he's always been very much a 'leave me alone to do my own thing' which I have done, I've mostly let them do as they please - for example only handling them to check on their wellbeing, or to catch them for vet appointments.

Additional info; they are in a huge cage with different floors, plenty of toys and pouches, and two suitable large wheels (on different levels so spreading out resources) and also get free roam access in the room they are in. I change it every couple of years with a new cage and keep a couple of their toys and pouches to keep their scent between new set ups. Room is always kept at 22oC.

There are other animals in the room but they have no contact - pygmy hedgehogs (in vivariums so the gliders cannot access them anyway) and ball pythons (also in vivs so the gliders cannot access them). I've had hedgehogs here since before the gliders, and the ball pythons have been there for over two years now so it doesn't match up timeline wise with the behaviour issues. I also have dogs that come in when I'm feeding the animals at night, but they're shooed out of there once I let the gliders out for their free roaming, so there's no direct interaction between them either.

Anyway so for the last seven years the trio have got along swimmingly, no issues. Always all clear at vet check ups. The male just likes to do his own thing and I leave him to it, whereas the girls will come out and hang out on me or explore the room, he has never wanted to go out of the enclosure. Always been good eaters, groomed each other and played together well.

THE MAIN CRUX OF THE POST / MAIN ISSUE - in the last few months the male has become extremely aggressive to the girls - he won't let them eat, he won't let them play, he starts crabbing as soon as they try to come near him and chases them away. Initially I didn't want to split the group up and tried giving them time apart during their free roaming (which, again, the male doesn't go out of the cage anyway and the girls were happy to get away from him) I've put different food bowls around to spread out the food, ensured there's plenty of it. He jealously guards the food, dashing between each bowl and attacks them if they go near any of them, it's like the mere sight of them eating food sets him off. He has also been overzealously grooming them to the point their tails were losing fur and starting to become patchy, his tail was fine. I had to stay and monitor them to make sure the girls were getting food and got to the point I'd take them out to eat away from him to give them some peace from him chasing them.

It was when I saw him attack one girl so violently he drew blood from her face that I decided to separate him. The girls are so much happier without him, their tail fur has grown back in, they are back to eating well and playing. They aren't cowering in fear in their pouches or dashing out of the cage to get away from him.
It's been three weeks since I split them up, and the male has since been kept separate from them, but within visual distance so he's not totally isolated. He's becoming more aggressive(unsure if this is just lack of confidence as he's alone now and uncertain) and launches himself at the bars if he sees me or my partner try to open them up to feed him, tries to bite my partner's fingers. He's been over grooming his tail and it's now a patchy mess. He frantically scent marks everything in the enclosure again and again. He is still eating and he uses his toys and the wheel, but he's clearly not happy.

Honestly I'm not sure what to do with him. I don't want to re-introduce him to the two girls as he will likely just go back to beating them up and resource guarding. I'm uncertain if introducing a younger, castrated male will help either. It's clear he isn't happy by himself, but I'm unsure if he's safe to be around other gliders again. I'm open to getting him on some kind of calming medication if such a thing exists for gliders, I do wonder if he's maybe got something going on with him internally that isn't obvious and that's caused his massive insecurity and aggression.

Has anyone dealt with this kind of thing before? If anyone has advice or words of support, I'd appreciate them!

Should say have been to the vets with him when he was starting to show this aggression and they couldn't find anything immediately physically wrong with him!

If you put them back together, put the feeding dishes on different levels and try to get the food in there before they get up. Putting in glider kibble so he can nibble on that may also calm him down as far as resource guarding.