[FF] Going nuts hearing about an unexpected night at my girlfriend’s apartment

My girlfriend and I have a bit of an exhibitionist streak. Not in real life, but really just online, so we have another reddit account that we use to post picture and short videos of ourselves on another
subreddit.  However, I can’t really share this story with anyone in real life and I don’t want it connected to my other account for a number of reasons, so just posting it here separately.  To be honest, my girlfriend would probably be upset if she knew I posted this, but I’m like 99.99% certain she doesn’t read this subreddit. 
She and I have been together since October of last year.  We are in San Francisco and we met through a professional mixer.  We started out as friends, but at the time, I was going through something hard with a family member who passed away and she was a huge support at that time.  The friendship quickly turned into dating.   We’ve always been very honest and straightforward with each other our whole relationship. 
I like that she doesn’t play games or dance around topics. She just says what she wants and it allows us to have everything out in the open.  She is very sex positive and progressive thinking and so there has never been any questions around that topic.   
Early on in dating, she let me know that on occasion she has a need to be with women sexually. She isn’t really into the idea of relationships with them, but sexually she has a need sometimes for the physical/sexual connection.  
When she first brought it up, it wasn’t like an ultimatum or anything where it was like “take it or leave it” but it was more that she was just being honest about who she was.  From the get go, I made it clear that I wasn’t there to tell her what she could and couldn’t do and I valued honesty as well and even if that was part of her, I liked her enough that I wanted to see where things went.  As we dated more, it wasn’t something we focused on, but we talked about it a couple of times and I came to the conclusion
that if that happened, as long as she was honest with me about, it was just part of her and didn’t need to take away from us.  She also told me that just because she had those desires I shouldn’t have expectations of it turning into a threesome. If that ended up happening, great. But if not, I shouldn’t get disappointed or expect it. 
My job goes in cycles and can be demanding sometimes.  The last few weeks has been one of those times.  Last Saturday, I was working late into the evening and my girlfriend was out with her roommates and another girl who they were celebrating her 30th birthday.  It was almost 11o’clock at night and I was finishing up.  The plan was if she was back to the apartment, once I got done with work, I was going to go over and see her like I frequently did on the weekends. 
I sent her the following text and her reply: