It's easy to understand why you're concerned about Simba, Jen. You obviously care very much about the health and overall welfare of every kitty you come in contact with. It could be that Simba feels a bit overwhelmed in new surroundings and new kitties to get used to. Be patient with him, once he completely settles in he'll feel more secure with you. Before you know it, he'll be asking you for more food. With you to care for him, there's no doubt that everything will be just fine.