Gf [F] and twin and their shared guy

So posted once on here before about me finding a bunch of saved iMessages on my gfs laptop. Lots of dirty stuff Dick pics, photos of her by other guys and just a crap ton of sexting. I didn’t know about hotpast until someone suggested I post it on here and now I think it’s my kink…
I started slowly asking her about the other guys she’s been with after we bought her a 9 inch “king Cock” dildo for her. I only got super curious after that because she takes the entire thing while we sucks me off. I naturally thought she must’ve had dicks like this before because it fit so well. Like very well.
So she starts telling me a few things at first, how many guys she’s been with and I told her my number. Then she told me about her anal obsession for a year. This goes on for weeks until she realizes I don’t mind hearing it, that I actually like it haha
So she tells me about this specific guy she was sleeping with back where her family lives and exactly how big he was. She didn’t know the exact number of inches so she showed me by saying it would hit me “here” when we had sex, she was pointing just above her belly button. Since we had the king Cock dildo at 9 inches and I’d used it on her now a lot I knew that it hits her right at the belly button! So I said that must be 10 inches because your dildo doesn’t go that far and she shrugged it off and said “I guess so idk”. That where it ended for now.
She calls her twin sister almost every single day on FaceTime to catch up since we live on the opposite side of the U.S. and they’re close they talk about everything. I knew this because I’ve heard her talk about me in bed with her and I’ve seen the Dick pic I sent her when we first started dating that she sent to her twin. So on FaceTime I was in the back listening and I brought up the huge dick guy amber used to see back where they lived and of course her twin says “oh Ricky?!” My gf blushed and said yeah him and I said did you know him?? Her twin said oh yeah we knew him with a weird smile.
I pry and say well wtf are you smiling so much for? And laugh. They both laugh and her sister says well I knew him first lol
I stoped and said waiittttt a minute you BOTH fucked this guy?? And they said yeah. So i asked how far apart and they Didn’t want to tell me the answer because they admitted it was at the same time!
So now we have my gf telling me about this massive cock she was fucking and now we know that her sister was fucking him too. I was dumbfounded. Didn’t know what to say. Her twin just straight up said next that “well he didn’t really fit in me so I didn’t do it long”. I looked at my gf and said well he fit in you! And she was blushing more than before because her twin didn’t know that haha her twin said “wtf he fit in you?!” And my gf replied after looking at me “yeah it took me a couple weeks but he fit all the way after that”
It all leads to the last comment my gfs twin made after that… she said “well that explains why he fucked us both at that party, I couldn’t fit him inside so he didn’t cum” “he must’ve came to you right after”
They both busted out laughing while blushing and saying wtf are we talking about right now I gotta go.
I’ll try to get more on that night but hats all I have for now. Feels like I opened up something good here and don’t want to pry too far to soon!