You see, Harumi, the problem here is that, when you and Chiaki started playing boobie-grope games, you forgot something important: you forgot to tell Chiaki that, first, before letting her touch your boobs, she had to tell you that she liked you -- and properly ask you to be her girlfriend.
Because you forgot that, the relationship between the two of you is a mess right now: nobody knows for sure what's okay to do and what isn't, what's cheating and what's not -- and that's how you end up in silly fights like that.