Im looking for a oneshot. Where this highschool boy writes on his desk and someone write b...

F O L L O W I N G

This doesn't have a the boy writing one the desk but the plot is similar to what you described:

http://www.mangago.me/read-manga/samishigariya_no_love_letter/

http://www.mangago.me/read-manga/miracle_time/

Main person is a girl, but is very close to what you're explaining.

I don't think it's this but it has the writing on the desk thing you mentioned
http://www.mangago.me/read-manga/junjou_romantica/

Yeah it's something like that. But it's a boy. I can't remember if they meet each other