Searching for this manga

I would like to ask what title of the manga this is, I have forgotten it so I thought of asking it to you all ^0^

I don't remember much but it's about a boy who fell in love with her sister's boyfriend, I remember that the boy and her sister's boyfriend was about to hang out together when he and her sister got into arguments that she was being unfair, and before that night he overheard her sister talking to her ex-boyfriend, he couldn't do anything but think about her sister's safety since her ex tried to assault her her once, and that's where the part when the boy told her sister's boyfriend to rescue her and he was left alone.

I think that's the part where things will get better, sorry for the confusing details I'm not good at explaining stuffs but that's what my memory recalls :)

It's a shounen ai, sorry for intruding and thank you for responding! ^3^