Looking for yaoi manga

Its about a college student who finds a little box in his bag and sees a note there. So he replies to the note and next day theres an answer. He ends up befriending a guy from the past who has a heart condition and they talkand fall in love. So they decide to meet in the main guy's time if the heart surgery went well. I cant find it so if anyone remembers id love you forever!

P.S. Is it possible to see allthe tags somehow? Like how do i even search tags if im not sure what os available?