About their past and their relationship

Yoshiki hated Tsukasa for a bit back in high school because he used to actually try in life till Tsukasa beat him in everything and he lost the will to try anymore, to get revenge he stole Tsukasa's first girlfriend by biting her neck to form a pair with her, the one who gave Tsukasa the trauma that makes him hate omegas, this caused her to break up with Tsukasa as Yoshiki had hoped so he went to go see Tsukasa in pain and when he saw him crying he fell in love with him. In the flashback Yoshiki says "maybe i just want him?". So, he realized his feelings and then started stealing Tsukasa's other girlfriends too because he didn't want Tsukasa to be taken. Given the dialogue, i also think it might be Implied that in stealing the girls after the first he was purposely making Tsukasa hate the type of girl he likes, omega girls, so that he'd consider dating an alpha, this is evidenced twice when he asks Tsukasa out in HS using Tsukasa's hatred of omegas as a sort of "I'm the better option" chip and during the start when they meet again coincidentally when he does the same thing. Yoshiki then asked him out, only to be shut down, they go their separate ways after graduation followed by their chance meeting outside Yoshiki's workplace, this actually was a coincidence as it shows him wondering how Tsukasa's been since high school as they haven't kept in touch. I think what Yoshiki meant by "even if it was all fake" is that when he approached Tsukasa for drinks he had every intention of luring him into sex as he was finally seeing the guy he's crushed on since high school again, then there's that he says he makes Tsukasa jealous on purpose by comparing him to his other lovers. He was acting like he only ever viewed Tsukasa as a friend, when he had every intention of seducing him from the start and he manipulated Tsukasa into feeling jealous and eventually into loving him. About the condom thing at the end, he didn't know Tsukasa could become an omega, the doctor says it's a very rare condition and Yoshiki never hints he knew about it, his intention was just to be with Tsukasa, that he can become an omega is just the icing on the cake and his yandere mind knows that if he makes him an omega he can bite him and that's it. Checkmate, they're mates for life and he can get him pregnant to keep him too. Him being an omega would just solidify his claim on Tsukasa. It's shitty that he's plotting getting him pregnant behind his back, but I don't think he has any intention of leaving him or treating him poorly like some people think.