Not only are you not betraying Maxie and Cosmo, they're probably the ones urging you to strongly to adopt "Tripod". Special needs cats, injured ones, sick ones, they're the only ones I've ever adopted, so I know how you felt when you saw this kitty. I say go to Reno, your sis will look after him while you're gone and while he's learning the lay of the land. I, for one, am ecstatic that you made this decision.