"Love", what a nuisance. [Love Allergy] a.k.a. Lovesickness Symptoms: Heart-shaped rashes ...
MC got a disease when young, one where he is allergic to love. Since then he has been taking medication that makes him unable to feel love. Then whabam, his doctor tells him he is cured and he can feel love again and his childhood friend confesses he has been in love with him and suffering from the same "lovesickness". It's a cute read.