Is AUTHOR wrong in the post ? POST : So my GF and I have been together for 7 years and we're planning to move in together next year (we're both 26).

His brother (32) recently moved in with his GF and never had a chance to have a proper housewarming dinner until now. We've talked multiple times about what to cook at said dinner, how I was gonna make his favourite cake (I'm a baker) and other general plans.

Last night my girlfriend let me know that the housewarming dinner was going to be held on thursday but that he wished to invite only family and that he specifically asked that I didn't come because it was too much of a special moment.

My Girlfriend also let me know that he didn't buy me a gift this year (when questioned he said it was weird to give gifts to your sister's boyfriend). 

I bought him a very rare edition of his favourite book but honestly I don't feel like giving it to him now, what he said and did made me feel like after 7 years I'm still not considered family and that hurt.

So AITA for not wanting to give him his Christmas gift?