This manga isn't Happy Play (Just checked that myself.)

But this manga is very similar to Happy Play:

Guy hates other guy and make fake love confession to the guy he hates,
and the hated guy tolds the fake confession guy that he loves him too (Not sure, but if i remember correctly the guys start to have sex on the confession scene.).

The fake confession guy gets his "revenge" idea from girls,
who were talking that the girl fake confessed her love to
the person she hated, so the guy asks her to help him.
And the girls are filming the fake confession.

Sailor Danshi ch3 (Pure-hearted Lies)

Thank You Very Much!!!! 😀
It's damn GOOD everytime i read it ^_^

I just wish i would have better name memory...