I believe your cat has been traumatized first with another brutal cat who came into home after your cat had been one and only. Good idea removing that cat. Second your cat is an outdoor cat, coupled with being beaten up, fleas, the move she/he
is afraid now. My suggestion to you would be put food and water near litterbox for a while. I believe that he is going to eat and drink and with litter box nearby within a range close enough as not to have any litter go into water/food. This is going to take quite some time I am positive this is going to work.