AITA for not being attracted to my girlfriend’s body?

I made an ALT account to ask this, since a bunch of my family follow my primary one. I’m also.. not completely sure of the rules here, so I’ll try to keep it as PG as I can.

So, me and my girlfriend have been dating for almost 3 years. We have fun together, and we really care about each other. (just to keep it simple.) I will say that she’s the first thin person I’ve ever been with. She’s flat, petite and pretty short. Most of the girls I’ve been with have been on the bigger side (in the good places..) and I’ve always been a fan of ... well, a bigger ~chest~ size. This all started when me and my girlfriend were watching Netflix a few nights ago and she randomly asked me if I was okay with her having a flat chest. (She’s always been insecure about not having b*bs.) I asked why she was curious about this, and she told me she noticed that I never really had anything to say about her chest, (and that day she had been trying on lingerie and none of the ones she tried on fit her in the *chest region. That kind of put her back mental funk where she thinks she’s not attractive if she doesn’t have a certain figure.) She said she was just curious. I told her I had to be honest, and said that I’m not attracted to her chest size, and that I actually prefer bigger b-bs. It’s not a turn off, having a smaller size but not a turn on. If I’m being honest, that’s why I usually prefer she faces away from me during intercourse. She was quiet for a while, and then she said she was going to go home since she had work in the morning. She texted me later on that night and told me what I said hurt her a little. She said we’ve been dating for a while and never brought this up, and that she feels like I lied to her. I told her I didn’t know what to tell her, and that I was just being honest (I was.).

Am I being the asshole here?

EDIT: Here’s an update, for people who wanted it. Ignore if you don’t care, I won’t be mad: https://www.reddit.com/user/waywiser86/comments/azskqk/aita_only_update/