Official version

Didn't he say in chap 9 that ML loved him and shouldn't have ? So I thought the "unrequited love" was about ML liking MC. But re-reading it, he also says that love is amazing so... who was in love with who ?

In this world, it's obviously ML fell head over heels for MC just by talking, pretending to be AI,. That's why I'm so surprised that in the original world, the guy in hood, MC's unrequited love is ML. MC must be misunderstanding then.
On my first read I still didn't know who was who yet so I didn't notice.

Spoiler alert:
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In mc’s original world, he realized the guy in the wheelchair (ML) had feelings for him. He could tell by the look in his eyes. But mc never accepted those feelings and was mainly attached to him because of his connection to the guardian lady. Idk if mc liked him back, he just felt comforted that someone was by his side

I think MC means the "found family" type of love that he had in his original world with people like the guardian auntie, Mr. Hwang, Seona, and even his version of ML.

Romantic love was never even a possibility in his original world, since he was either on the run, at war, or just plain worn down from losing people he cared about.

You got it backwards, it was the ML who held unrequited love towards the MC. The MC knew but he never returned those feelings, he just stayed with him out of obligation.

He fell in love with the ML in this new world.

Oh.. So everyone got it right except me. Haha. ٩(๑❛ᴗ❛๑)۶
Now I am glad I raised this topic so i can get it right too and thank you for spoilers.. Anyway I still wonder if ML never has romantic love, how come he knows " love is an incredible feeling but unrequited love is terrible."

Wait? Eh, so then who’s the duck that uke was sucking his his previous world? MC says he is really good at blow jobs. If he isn’t sleeping with ML of previous world. Is he just banging whoever?

Pretty sure it was just MC messing around.

There's a part in the novel where MC and ML are talking about sex-guiding and MC claims he's had 20 partners. ML grumpily says he's had none, since no guide matched his wavelength. MC then realizes that ML thought he was being serious and is about to admit he's actually never done sex-guiding, but they get interrupted.