AITAH For leaving the house in the middle of the night after my girlfriend laughed at my size?

NSFW
My girlfriend (22F)and I(23M) have been living together for 3 years now. Everything has been fine until now. I guess we had our first “big” fight of the relationship. My girlfriends day off was coming up and she was going out with one of her girlfriends for most of the day, so I wanted to make a romantic dinner at home with candle light and everything for when she comes home, then have it end with some fun in the bedroom which we haven’t had in a while. I’m a bit of jokester, so while out buying groceries, I stopped by the adult sex shop about 10 minutes from our house and got a sexy cowboy get up. Really it was some leather straps with tassels, boots, and a cowboy hat, with a speedo type underwear with a “open” front for your member to hang out. To me this was hilarious and thought she would find it funny and cute. Not so much a turn on but little jokes are my love language. Well the dinner was made and she came home to a big surprise, we ate and enjoyed the romantic dinner and then I told her I have a surprise for her. I told her to wait there and I’ll be right back. I went to go put the costume on and then I said, “are you ready” then strutted out with the cowboy get up on in full Clint Eastwood mode. My girlfriend started to laugh hysterically and so I kept up with the act and asked her in a low cowboy tone “do you need help with the cattle Mamn” which she then replied with, “why does it look like that”. I was confused at first so I said “what, the costume” and she said “no, your penis, why does it look like that”. I looked down confused and asked her what she meant. She proceed to ask my why my member was so small. This took me by surprise because we’ve been together for 4 years, living together for 3, she has seen my member many of times. Most times obviously not soft, but I’m sure she’s seen me fresh out of the shower and so forth. I asked her again what does she mean by small this is how it’s always looked when I’m not hard. She then laughed again and tells me she’s just never noticed how small I was when we’re not having sex. This kinda hurt my feelings a bit but I tried to lighten the mood with a joke as I do, but this is where it goes down hill. I made the joke saying “well this rattle snake will grow once its starts rattling” in a another cowboy voice which she giggled too and said “I hope so because I’m used to more then that” this struck me as odd for some reason and I unfortunately asked wdym? Now thinking back, I shouldn’t have asked that, but she then proceeded to tell me that all the other man she’s been with were all hung even soft. So she wasn’t use to seeing one so small. I am indeed and grower not a shower but this really hurt me. I then dropped the cowboy act and became pretty insecure. I’m normally okay about this topic but idk, I just want expecting her reaction. I felt embarrassed and she noticed that I was clearly uncomfortable. I then left and put some PJs on and started to clean some dishes to which she then made her version of a joke saying “is the little inch worm upset now” as she giggled. I kinda just froze and asked her why she would double down and say that. She told me it was just a joke and to get over it, but now at this point in my head I’m thinking all over the place about my size and her exes and if she’s even satisfied with me. So I asked her if I even satisfy her and she then tells me “sometimes” but then tells me it’s not a big deal for her, we begin to argue more about it until I tell her imma stay with a friend of mine for the night. She then texts me telling me I’m an asshole for leaving and won’t listen or try to understand her point. AITAH?