Eleven03

Basically, they're both just stupid the MC doesn't want people to figure out he's gay (and has been in denial all of his life up until chapter 1), so he wears a ring on his finger to trick people into thinking he's married.

MC also happened to be ML's gay awakening (assuming he didn't know he was gay before their time in the military). ML lowley falls in love with MC because of this, but then MC starts acting really coldly to ML because MC struggles with internalized homophobia at this point because he wants to be "normal" (in society's eyes).

When they meet again for work, ML sees the ring and believes that MC is in a relationship, and MC is kind of dumb and forgets that he has the ring because it's such a regular part of his life.

It's been a while since I've read this, but the whole misunderstanding is that ML thinks MC is in a relationship and MC never tells him that he isn't even as they start sleeping together

so ML thinks MC is a manwhore and MC isn't doing anything to deny these ideas because he wants ML to think he has experience (they were both loser virgins)

huhu but i’m already 30 now and they still have misunderstanding how long does that end

the misunderstanding is the whole basis of the manhwa so it's not going to end for a LONG while it gets a little exhausting but it's still fun to read about how much they confuse each other if you're into that