<human>: So me and my girlfriend decided to buy some ikea furniture and organize our living space a little bit. A lot of her stuff had been piled into my room and was kinda messy so we bought a cabinet for her to keep her stuff off the ground. 

well while she was cleaning up the rest of her stuff, she showed me a pair of underwear and said "do you know who these belong to?" and I just sat there blankly and said "no I don't, why? does it belong to [either one of my two girl roommates]?" 

she just looks at me coldly and says "No....I sent them a snap of it and asked them and neither one of them said it was theirs" This is when she gets silent and starts to shut me out. I get it now. She thinks I cheated, but obviously doesn't want to directly say it. But now she's demanding I figure out how they got there, and is essentially giving me the cold shoulder until I come up with an explanation (like that's my fucken job. it was under her pile of clothes).

now I'm just sitting here typing this up alone while she's spending the night at her friends house. Just for the record, I did NOT cheat. And I really honest to god don't know where in the bloody hell they came from. And now I'm at a little bit of a loss because she won't accept the possibility of it getting mixed in at the laundromat or any other plausible cause.

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: Girlfriend found a pair of underwear that wasn't hers while cleaning. Thinks I cheated and is trying to get me to admit it