He gonna lock him up

Not in the least?

Out of all the possessive semes I've read about Yoonsung is by far the least psychotic or possessive lol

He's worried about Ha-kyung being hurt or suddenly vanishing like he did last time, sure, but that all stems from his trauma coupled with the failed suicide attempt and near death experience. It's not like he's an obsessive stalker lol

Excessive possessiveness does not necessitate obsessive behavior. Consider his actions in locating Ha-Kyung during their separation on that rainy night. While the label of "stalker" may be contested, the intensity of certain actions is undeniable. His trauma-induced fear of loss is acknowledged; however, it's equally important to recognize potential psychological instability.

We can only await further narrative developments.

You said it "borders psychopathy and insanity" but you don't just become a psychopath. It's usually something you are born with or comes with some sort of physical or mental trauma which also comes with an almost complete personality change.

Him stressing about Ha-kyung's safety, which is warranted given his family and how far they'd go to remove Ha-kyung from his life permanently, is perfectly normal for someone who is so deeply in love. I'll admit that he does need help with dealing with his trauma, but he's nowhere near just locking someone up. He isn't restricting who Ha-kyung can speak to nor is he barring him from leaving the house. It's not like he's got separation anxiety either given that he's still actively going to work and doesn't meltdown if Ha-kyung leaves his line of sight.

I think you're reading too much into this tbh. I can see him asking Ha-kyung to contact him frequently if he leaves the house till his family finally backs off, but he's confident now that Ha-kyung won't just leave him so there's no reason for him to be possessive or overbearing to the point of abusive behavior.