I LOVE THE PLOT TWIST! So, to explain the ending, Yoshiki was jealous at first of Tsukasa’s girlfriends, so he stole them secretly, and he liked how Tsukasa was crying, so he continued it. He’s probably a sadist based on his reaction. And at the end, he pierced the condom in order to impregnate him, I guess, if Tsukasa turned into an omega for real.
Imitation Mate