I've read this post about a dozen times and I still don't understand it at all.
The title is "my girlfriend almost broke up with me", so I expected some kind of story of something that happened that would cause his girlfriend to break up with him. I was greeted by little more than word salad.
I'm not even entirely clear on the story, but what I think happened is that you, your girlfriend, and another girl tickled some boy? There is no antecedent to the word "him" besides "the principal," and I assume you were not all three of you attempting to tickle the principal. Regardless, I assume that means there was a boy there, then your girlfriend, another girl, and yourself. You then proceeded to effectively gangbang him with tickles, and got in trouble. I can follow that far, I think. Then you throw this mindbuster at me: "and now I don't want to do that anymore." Do what? Tickle people? Step on peoples feet? Have a girlfriend? What are you referring to?
And more to the point, how did any of this make your girlfriend want to break up with you?