TIFU by thinking my grandmother wanted me to take part in a threesome

Well where to begin with this one.

I(27M) have been talking to a woman I met online for a little while now. Nothing official yet, but just casual conversation and some flirting that does get dirty now and again.

Well today I texted her asking if she would like to meet in person to get dinner or go to the movies. She said she doesn't go to the movies but dinner would be great. I thought it was a little odd because a week ago she mentioned a movie she wanted to see. I figured she just doesn't prefer it for a date night, or waits until she can watch from home.

I say dinner is perfect and ask what day is the best. She tells me and asks "Do you want me to invite Papa or just you and me?"

I'm stunned with a bit of confusion at this point. She had never mentioned having a boyfriend, husband, or "Papa." I responded to say "Sorry I don't know what that means."

She didn't respond for a bit. So I decided to be a bit more straightforward. I asked "Are you asking me if you can bring a boyfriend? You never mentioned being in a relationship so I wasn't sure who you were referring to."

I know it's more common now to see open relationships or throuples. Not something I've ever been a part of but hey, you never know.

At the same time I sent it, she responded "Sometimes grandsons want me to bring Papa along, sometimes they just want to see me."

I was really struggling with these code words. I've heard of unicorns, but Papas and grandsons? I have no idea what these terms mean and what sex club or orgy was awaiting me. But I wanted to learn more before outright refusing.

I said "I'd rather just meet with you. If you and your boyfriend are okay with that."

Again, silence for quite a few minutes. I'm scratching my head wondering how we went from normal conversation to nicknames and innuendos I've never heard of.

I start typing a new message to apologize and explain my confusion: "I'm sorry, I'm just not really familiar with this terminology. I don't mean to be forward but are we even talking about literal dinner? Or are you asking if I want to join you and your boyfriend in the bedroom? I'm sorry I'm just confused."

As my finger moves towards the send button, a text appears and I hesitate.

"I think you're texting the wrong person."

I assumed she was getting frustrated with my ignorance on the subject, and decided to just send me on my way. I shrugged it off and thought I was probably better off not pursuing it any further.

Then I scroll up on the messages.

I realize with pure horror that I've been texting with my grandmother this entire time.

I'm really really bad about adding numbers to my contacts. I usually know by the area code who's texting me. Well my grandparents and my new lady friend share the same area code. No one else I contact has it.

Pure panic washes over me as I try to reconcile this conversation I've just had. How could I be so stupid? Papa is what I've called my grandfather my entire life. I'm her literal fucking grandson and I'm trying to figure what the word grandson means sexually.

My grandparents are literally the picture perfect sweet old people you think of. They are not ones you would ever use profanity or discuss inappropriate topics with. They also wouldn't be okay with an open relationship or throuple situation. They are way too traditional for that.

I pledge my entire future genealogy to whatever higher power intervened before I hit send on that last text. But I'm still terrified. I just asked to meet a girl without her boyfriend, if her boyfriend was okay with it. How do I explain this without looking bad. Also how do I explain my interpretation of "Papa" to mean boyfriend in the first place?

I call my grandma. She answers and thankfully is not freaking out as I expected. I tell her I was just texting a friend to hang out. I wasn't aware she had a boyfriend, but I was still interested in catching up over dinner if he didn't mind us doing that. She seemed to buy it and laughed off the misunderstanding. She said something about it being funny that I thought Papa meant boyfriend, but I didn't want to spend any time on that topic.

Crisis averted. But for a minute there my life flashed before my eyes. I'm so traumatized that I can't even bring myself to ask the right person out.

TL:DR / TL : DR

Texted a girl asking for a date. Turns out I accidentally texted my grandma and thought her use of the words "Papa" and "grandson" were some innuendo referring to a threesome or throuple. Caught my mistake just before I outright asked if a threesome was happening. Too traumatized to ask the girl out for real.