For those who don't seem to understand what was going on in this chapter:
Whenever Honoka finds out that Noriko got a new boyfriend, Honoka would seduce the guy into dumping Noriko and dating her in secret, only to make Noriko sad and come to Honoka for consolation. After which Honoka just dumps the guy since he's rendered useless.
So yeah, it was pretty dark move, only to get some coochie from her girl-friend.