I've had a lot of time to think about what happened yesterday. I've also read through a lot of the comments. Thank you to everyone who gave me advice on what to do. There's been A LOT of development and a few requests to follow up, so here it goes. It's whatever at this point.

We had been texting off and on all evening. As promised, I agreed not to bring it up in person. When I got home after work her car was in the driveway and her sister's car was there as well. I was a little nervous not knowing what I might be walking into, but overall I just wanted to get whatever was going to happen over with. When I walked in it was clear so did she. Her sister was helping her pack up her things. I didn't know what to say, but I never expected this. I honestly thought everything was going to be okay when I got home. Her sister just looked at me and didn't say anything.

I walked by her sister and went into the bedroom where my girlfriend was. She didn't say anything either. She didn't even look at me. If she was going to leave I at least wanted us to have a discussion about it. Everything I had read in the comments about buying a bidet and OCD lead me to believe there might be more to all of this than I had considered. I started to talk and she just threw down the hangars of clothes and screamed at me. "YOU PUT THIS ONLINE? I TOLD YOU TO NOT TALK ABOUT IT!" Her sister ran into the room and told me to just leave until they were gone. She then accused me of cheating. WHAT? This whole thing has been crazy and I feel like I had dealt with a lot up to this point but man that was it. I snapped.

I told her sister I had never cheated. Not once. I would never cheat on her. Enough was enough, so I told her sister the reason she was there was because earlier I had found out my girlfriend had been going to the bathroom and wiping herself with my socks. Everything went silent. Like, no one said a word. Out of nowhere they both start crying. Her sister stared yelling at me and told me I shouldn't be talking about things I don't understand. When I asked her what in the world she was talking about she just kept on yelling at me and shouted back that it was normal and that I need to mind my own business.

Her sister knows about it. (She did not know I posted on Reddit about it)
Her sister thinks it's normal.
I need to mind my own business? They're MY SOCKS!

I stood there all kinds of messed up so I just left. I went to a buddy's house and stayed the night. I also called off work today. I went home and all her stuff is gone. I didn't text her back. I think I'm done.

To clarify a few things: She insisted on doing laundry to keep my suspicion of her not having many socks at rest. She told me last night through text she always throws away the socks and never washed them. She reaffirmed it's not a fetish. She won't try a bidet because she doesn't want poop water splashing on her. I can't keep up with the comments. I'm pooped. (I'm trying to find humor in this because I'm really upset :(

So yeah.

Edit: (a sentence) Her sister did not previously know I posted about it on Reddit. I'm sure they both do now.

Sauce: https://www.reddit.com/r/relationship_advice/comments/aw9dzh/update_i_28_think_my_girlfriend_26_has_been_using/