I really am not sure about this but maybe this one http://www.mangago.me/read-manga/dekiru_otoko_ga_suki_nanda/
it's been a really long time since I read it so I am not so clear on the details...
I think it's chapter 4-5 of Katekyo by Moegi Yuu.
I know it too but got no memory of the title .
Im not remember it clearly. The seme and uke are friends and they are growing up together. The seme trying to be perfect so that noone will interest in the uke. There is one time that uke receive a love letter and seme tear it to pieces before the uke tell him that the letter is for the seme not for him.