You have not had him long enough for him to trust you, you are a scary predator so when you put your finger in his face, he bites the scary predator.
1. stop putting your finger in his face.
We have a few gliders we can pick up. we have some I have to scoop up, or better yet I put my hand out and let them walk on me of their own choosing. But the ones we have for awhile dont really bite anymore, they give a small nip if I try and pick them up and they don't want to be picked up. About 4-5 gliders out of 10 I can pick up and they might not like it, but they wont bite.
I would start by sitting at cage and talking to your glider, maybe get a tasty treat (yogurt drop or dried mealworm) to try to give to him. At first he will grab the treat and maybe bite you also, so give him as much length of dried mealworm as you can, or offer the yogurt drop on a spoon. He will grab the treat and run away fast. After some time, he will start to take the treat slower, more carefully. over time (maybe months) your glider should start taking the treat nice and easy with no chance of biting you. Our least bonded one will now take the mealies from the palm of my hand without biting me. you can feed the treats at night when they are awake.
another thing to do..
Just before awake time, get a glider safe small room, take out sleeping pouch with glider in it, take to glider safe room or tent. sit in room, with lights turned down low. if your glider does not come out you can gentle force him out of pouch. Let him explore, keeping sleeping pouch away from him. to start maybe keep this time short, 30 minutes. then when time is up offer him the sleeping pouch, he will probably jump right back in it. during this time just talk to him let him be, no finger poking, offer him a treat.
it shouldn't be long before you can pet him on his back. But picking up is hard and depended on the glider and bonding time and trust.
I usually let the gliders walk onto my hand, up my arm to my shoulder, I then walk them to the kitchen (im up to 3 at one time) open the frig and get them some LIVE mealies, they love these. then walk them back to cage, or if just one I let him sit with me awhile.
Gliders lined up for my wife for dried mealworm time.