If they are going to, then they'll need to while Kiyo is away.The cover page being a shot in the chapter in an inspired decision.
In the end... Momoko's actions were led by the simplest reason... a broken heart (they are "roommates"), and was kinda childish but it was her feelings, nothing wrong with that, sometimes people need the time.
But... happy that she let it go and accepted the imouto and gone back to her (girl)friend.
They want to bang each other, you know it, I know it, the author knows it... fuck you fight.