It's possible to recover from certain types of allergies though it's very rare for food type allergy to dissapear. Also it's very dangerous because what Kasius did makes more harm to body than good, and person can die in the process. As for recovery I've heard only of respiratory allergies that...
I have forgotten what was going on, since there are so many side characters in new arcs with their own story. Might pick it up again some time later and read from the start
I think he pretended to be Isolda, wearing dress and etc so he could run away somewhere and cry when things got too tough for him. Since, as an eldest son he wasn't supposed to be a crybaby. Can't wait to see when real Isolda comes to their wedding and Leah throws herself at her XD