"I broke up with my girlfriend last year."
What part of this sentence differentiates between "her breaking up with me" VS "me breaking up with her"??
In case the other comment isn't clear enoug: this answer uses the speaker as the implied subject. When we want to reverse the action, however, we now have to specify ourself in the sentence as who was 'broken up with'.
This from a relative noob to the language, I'd appreciate it if anyone more versed than me would correct any mistakes I've made.
The "to" after girlfriend indicates she was the one who was broken up with, as "to" here means "with".