I love the little detail in this chapter where they were wearing their ring on their left hand when they were on their date. In contrast, in the office, Yui was wearing it on his right hand and Masugu didn't wear any.
Actually, it has already been revealed in chapter 2, page 20. Because he spent all his life on the battlefield, he turned down all marriage proposals and never married.
Good manga but the ending could have been better imo. Not much of a fan of loose ending like this (Maybe there's a chance that this will be pick up again once the author return to health?). The fireworks confession block is really cliche and unnecessary. There is nothing wrong ending it with...
chapter 1 & 2 is a one shot before they get serialized. You can find it here
https://mangadex.org/title/abad18cf-bf72-4bbc-97c8-b55dfa28f9b9/ane-no-yuujin