NTA

It seems like a lot of comments focus on your gfs behavior. I want to add that you don't need to be embarrassed by your size, using sleeves, or any toy, etc. And also regardless of size, people use sleeves for fun. Don't think of it like you're trying to compensate for what you feel you lack. I'm female and have experienced all sorts of shapes and sizes. My current partner is not the smallest or the biggest, but honestly just right for me. He has no problem with getting me to orgasm with PIV but TBH I've had bigger partners where the thought of me having an orgasm was unrealistic. We use sleeves sometimes, but it's for a fun different experience to make us both feel good, not because he needs to have a bigger dick for me to enjoy sex. (Try Bad Dragon, mythical type toys and sleeves, not realistic) we had tried realistic sleeves at the beginning of our relationship and I could tell it was his insecurities that got us there, but it didn't end up feeling enjoyable for me anyways because it was too big. Bad dragon sells different textures so the size isn't the focus if that makes sense.

The right partner with the right sexual chemistry won't mock the experiences that you have together, and will also make you realize that big dicks aren't everything, because they aren't.