is there any yaoi/shounen-ai manga that both party were in relationship with others and th...

The Walker series (starting with this one: http://www.mangago.me/read-manga/are_you_enemy/ ^^ If you look at the Comments on the manga's homepage, you'll find the order of the series)
You'll find that kind of plot often in this mangaka's works ;)

Thanks ヾ(☆▽☆)
i'll read it