I definitely think he was testing and provoking the Kouta in the beginning--Haruto has a strong manipulative streak in him. He knew Kouta liked him but Haruto is used to being pursued.
Finally, Kouta has permission to express his affection openly, like his past gfs.
Kouta, on the other hand, had zero expectations and acted like it. Instead of Haruto getting to bathe in the sunlight of Kouta's grateful adoration, he's getting drunk at another guy's place and telling him to forget the confession Haruto worked so hard to hear in the first place. lol, it was the first time Haruto ever had to be in pursuit so the cool facade crumbled.

I can't help but wonder if the seme was trying to provoke uke with that string of girls into saying something. That or the mangaka had a decided change of mind as to his character. Because his behavior is sort of strange if he not only was aware of the uke's feelings but actually returned them for some time.