yes this one http://www.mangago.me/read-manga/follow/
the sister : http://www.mangago.me/read-manga/itaike_na_bokura/
i like those. i'm collecting them for personal purpose and there's quite a number here http://www.mangago.me/people/tag/49344/amazing+secondary+characters/
Any yaoi manga with a very supportive female character? It'd be nice if the girl is a friend/sister/someone of one or both of the characters and supports the two guys.