I've been searching through all the tags I can think of but just can't find it.

It's a story at the end of a collection. Possibly in two parts? It's from the boy's perspective. He feels like his little sister hates him but she's actually in love with him. He's older and she's high school age? She's petite with long dark hair. I think he gets jealous when she hangs out with someone else. They're step siblings or maybe one was adopted when their parents died.

It's not Suki to Ienakute (Can't Say I Like You) from Dakishimete Ii desu ka. It's less smutty or not smutty at all.

Thank you for your time.