Is his vision problem resolved? Or is he still relying on Alissa to do a big part of his job? Do you think, because you have ten years of experience there, he feels threatened by you to end up with his job? But he doesn’t feel threatened by Alissa because she doesn’t have enough experience to actually replace him?
It just sounds like something more is going on here than you and Alissa both had an isolated bad days and behaved rudely to each other. It just seems like something bigger must be afoot to change the relationship dynamic between you so dramatically.