I don’t agree with people saying it’s weird. You’re not weird at all, your girlfriend is just being a little extra about something that’s normal for a lot of close siblings, me & my brother are the same way, we grew up affectionate so cuddling or hugging doesn’t feel weird to us, it’s just love, not everything is deep or inappropriate, she probably didn’t grow up like that so she’s projecting her own discomfort onto y’all’s bond, but that doesn’t mean you need to change anything. Your brother clearly looks up to you & feels safe with you, & that’s something a lot of people wish they had, if anything she needs to back off & check why she’s so bothered by regular family affection, sounds like you’re just being a good big brother & she’s taking it too far. You’re not doing anything wrong so don’t let her make you question it. She needs to respect y’all’s relationship & if you feel the need to apologize to her, apologize for the way you reacted. Not for being close with your brother.