Hahaha, you're so late. You missed the whole debate/comments on how Hyesung's pregnancy came to be.
No, he factually didn't and there was never a "debate", just informed people informing others who got confused. Hyesung got pregnant during the scene where he came in and gave Dojin a blowjob and said he wants a baby. It explicitly shows this in the manga at the bottom of the page here: http://www.mangago.zone/read-manga/love_is_an_illusion/uu/love_is_an_illusion-chapter-20/3/
OOOHHHHH! AH, I get it! Thanks, that makes a lot more sense!
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No problem :^)
But we have to say that he DID knotted him to make him pregnant and make him stay. But Hyesung was already pregnant.
He was in heat, that's what alphas do when they're in heat. It wasn't on purpose, he explicitly says this in ch 20 when he apologizes. Hyesung also says "his eyes... Get ahold of yourself!" because he saw Dojin wasn't in control. When he released his pheromones he lost control. Remember how when Hyesung went into heat he was still able to talk and move, but he was all about sex? Same here, those weren't Dojin's actions, he stops as aoon as he comes back.
WOAH OMG! I just noticed that Dojin impregnated Hyesung to make him stay with Dojin!