I get it. Me too. Like it's an intimate moment for them. That they want to f*ck not just to satisfy their bodies but to confirm that they are on the same page now, somehow a physical proof that they will be together to surpass this. No more sacrifices, no more leaving someone out, just them.
For me the lines were not cringe coz If I were Mieum, I would feel that Jitae wants a confirmation that no matter the circumstances, he is there for him. that for those years that he is careful with who he associates with coz maybe they're spies, he found a safe haven from Mieum were he can be vulnerable.

everyone saying the last lines where cringe and usually i agree but idk something about how they love each other so much and wanna be as close as possible is so endearing to me that even though it’s smut it sounded so sweet to me? does no one else feel this way? like it’s not just sex they are having but something more. feels kinda sad that ppl are just brushing it off as cringe