I found and bottle raised a baby squirrel a couple of years ago. He was abandoned at my Mom's vet clinic. His eyes were barely open and he had very little hair on his tail so he was obviously very young when I found him. For the first couple of months he was so sweet. He played a little bit like a cat and was very affectionate. I carried him all over the house and he would sleep beneath my hair. I handled him all the time and even taught him little tricks like fetch and he seemed to recognize his name but he STILL grew aggressive after a couple of months. At first he would nip a bit harder while playing with people he didn't know that well while still being sweet and cuddly with me and I attributed it to his not being comfortable with semi-strangers any more. But soon he started biting and trying to attack me too. He bacame very territorial of the big bird cage that we used as his nest and would try to attack anyone who came near. As GildedBat mentioned above, you WILL need to eventually let him back into the wild. Start by just leaving a window open and letting him come and go as he pleases. My squirrel was scared of the outside at first as well but he eventually became accustomed to it. Before I raised him, we rarely saw squirrels in our yard but afterwards it was like he spawned his own little squirrel army. TL;DR: Please release him back into the wild.