
I don't think Sunbae is a green flag buuuut one thing I don't get about mangas is why Gunjoon expects Sunbae to completely change once they start "dating".
Sunbae has consistently been like this. Gunjoon is the one who actually hasn't shown consistency, starting out from randomly judging and hating on Sunbae to then falling head over heels.
This is like the same logic of "if we have kids our relationship will get better". NO IT WON'T??? Just because the status of your relationship changes doesn't mean the individual will magically become a different person???
Do I endorse Sunbae behaviour? Fuck no. But Gunjoon ain't right either.

No girl would leave a girl alone when she knows there's a potential creepy lurking around.
I don't get why the princess leaves first saying "I have to go". WHERE??? YOU LIVE IN THE PALACE??? WHY WOULD YOU NOT ESCORT THE GUEST YOU INVITED OUT KNOWING THAT YOUR BROTHER IS A DAMN CREEP???? WHAT????
Also the prince constantly getting physical with the FL and the FL is just like, "yeah I'll be fine don't worry". Like girl?????? Tf??? You remember your past life when the duke asks to date you but you forget when you're dealing with a creep????????
Man. There's a difference between giving someone the benefit of the doubt and just being plain stupid.
The prince yanking her hand all the time.and no one doing anything about it, least of all the FL herself, pisses me off. Enough of the stupid damsel in distress trope.

Juheon knew he assumed shit about Doyun liking him, , Juheon knows Doyun can't process emotions the way normal people can.
I get the first reaction of Juheon being pissed and leaving. What I don't get is Juheon acting like an asshole 2 weeks later when he's had time to cool off a little. You can't just say I'm mad so I'm going to forget literally everything I've learnt about you as a person.
Imma still say Gunjoon needs to have more self reflection. He's not wrong for expecting the things he does from sunbae but he is wrong because he doesn't do those things himself and kinda unilaterally expects honesty, communication, and love.
Hopefully now our boys understand the importance of active communication