I'm going through my girlfriend's dirty laundry
Do you do this often?
Yes, she doesn't know I'm going through them
You should never go through someone's possessions without their permission. It's one thing to separate the laundry if you are doing the wash, but sifting through the laundry for any other reason is rude.
It's not that bad, and we are going to break up soon anyway.
Why are you breaking up? I think it's especially bad because you two are going to be together and you're still going through her laundry.