Why won't my cat go to sleep at night without me?

by Anastasia
(Utah, USA)

I have really bad insomnia so I don't go to sleep until 2 or 3 am or later, so I stay up working until I'm sleepy. The problem is that my cat (Marshmallow) won't go to bed without me.

I know he naps perfectly fine in the daytime alone, and I can tell when he's in deep sleep because he gets into weird positions and snores.

Yet at nighttime when I'm working, he sits next to my chair on the hardwood floor in that "feet tucked under tail wrapped around" position and every time I stand up for whatever reason, he's under my feet and trying to herd me to bed.

I've tried setting him on my lap but I hunch over my work too much and he tends to get squished. I've also tried cuddling him in bed until he's snoring and then leaving, but then a few minutes or if I'm lucky hours later he'll be right back.

I feel bad for keeping him up, but he usually doesn't even stay with me the whole night and goes to cuddle my mom or sister in completely different rooms.

Do I need to be worried about this? Is there something I can do to get him to understand it's okay to go to bed without me?

Any information or advice you have will be greatly appreciated. (Side note that I'm not sure if it's important, but he was abused by a previous owner which, according to the vet, gave him brain damage and he is a neutered indoor cat about ten years old).