Me (M23) and my gf (F25) have been together for around a year and a half now. Our relationship was pretty great, so I was blindsided when this happened. Around 1 year ago, I went on a trip with my family across the world. While I was there, she texted me (while I was sleeping) that she was going to go meet up with an old 3-month fling of hers for drinks that night, and they were just friends now. She also said "he's dating now" and if I was uncomfortable with it that she wouldn't go.
When I wake up to read this text I say that it's ok for her to go and I appreciate her asking me, but when I check her location she is already at a restaurant. I'm kind of sad at that moment because she never really waited to see if I was okay with it, so I just go back to sleep. And when I wake up again she's at her apartment. I call her and she doesn't answer, and she texts back that they're just talking in his car outside and she'll call me soon.
After like 10 minutes she calls me and says tells me everything that happened, how he picked her up, took her to a really nice place for dinner and drinks, paid for the bill, drove her back, and even asked to come up to see her place (which she said no to). She also said that when they were texting earlier he had asked initially just to bring a wine bottle to her place and they could have a "wine night." I was pretty upset about this and I told her that he clearly wanted to get with her again, and she said that she didn't really think about that. We change the topic for a bit and then she hits me with a "Babe by the way he has the biggest dick I've ever seen!" and I just grab my head and say ask her why she would tell me that and "I really don't want to think about that." I say that I gotta go and we end the call but I'm pretty much holding in the panic attack for the next week while I'm still on vacation. She posts a picture of her in the dress from that night on her insta the next day with a caption "dinner dress" which also definitely didn't help.
When I get back I bring it up again and explain to her how this is pretty much an actual date that you went on with this guy outside of the fact that neither of you called it that and she agrees. At first she's a little defensive and says that he said he wanted to meet her on the Dec 31st and I should be happy that didn't happen, and in my head I was fuming. Later she also mentions that she never said she had a boyfriend while texting, but talked about me during the date. She also said that he asked to come up to see her place after the dinner and she said no. She apologized for doing it and said that it wouldn't happen again and she wouldn't text him.
I told her that I forgave her but I'm having a hard time with some things.
Why did she text him and plan dinner with him without texting me?
Why didn't she wait to make sure I was okay with this beforehand?
Why didn't she mention she had a boyfriend while texting?
Why did she say "At least it wasn't new years"?
and most importantly,
Why did she tell me he had the biggest dick she's ever seen?
That last question has especially been messing with my head lately. I'm pretty sure she didn't say it with malicious intent – I think she just forgot I was her boyfriend for a second and blurted it out. It's been a year and I still can't get it out of my mind. I don't know how to address this with her. In her mind I've already forgiven her and by now I should have made my peace with it but I'm really not sure what to do.
TL;DR Girlfriend told me her old fling had a huge dick by accident, and I'm not sure how to emotionally get past this.