Osananajimi ga Yokkyuu Fuman de Komatteiru.

Three months after Naoya blurted out a confession to his childhood friend, they've started holding hands, kissing, you know, the usual boyfriend starter pack. But recently, his boyfriend Shuichi has been afflicted by a severe thirst that only Naoya can quench - can he get over his fear long enough to put them out of their suffering?
(Source: Futekiya)
Note: Includes an extra chapter.