ff
Following~
http://www.mangago.me/read-manga/pochi_to_tama/ their story starts at ch4 but it would be better if u read ch3 too..
similar stories:
http://www.mangago.me/read-manga/darenimo_aisarenai/ (they fighted over a girl in the past(if i remember correctly))
http://www.mangago.me/read-manga/rival_ni_ki_wo_tsukero/ (they fight over the uke but they end up falling for each other)
http://www.mangago.me/read-manga/renai_kyoutei_nukegake_nashi/ (same as the one above with a difference that i cant expose)
any yaoi where the uke and seme are rivals and trying to win the same girl but end up falling in love with each other?