Sounds like this little guy just needs time to see he is loved and that you are there when he is ready along with his new fur sibling but it's going to have to be on his terms... I mean put yourself in his shoes... First you are abused then you get another family that loves you but next thing you know you are placed in a scary shelter and now he is with you... Heck I would be scared to death to get close to you guys at first too out of fear you would leave me too.... Poor thing just give him love and let him know you are there when he is ready to let down the walls.
I now that answer does not help much now but in the long run I hope it does
