Can't remember a manga

This will be a shot in the dark... and the only thing I can remember is 1 specific scene:

I cant remember if this character was a younger brother, nephew, family friend/young non-relative, but he essentially interrupts an older guy about to have sex with his boyfriend. He doesn't leave right away and I think tries to ask a question - and this is the panel I remember - the older guy looks over his shoulder at him, and goes, "hm? What was that?" with a "get the fuck out" face. I think in context of the story seeing this older guy interact with his bf helps him come to terms with his own feelings I assume for someone else? I cant remember if its a spinoff, sequel or what. Its not a very recent manga from what I remember. I think the older guy did not date men before his bf but is very protective over him.