My girlfriend is really sad because I ditched her birthday to be with my sister. AITA?

I (22M) have been with my girlfriend (21F) for over 6 years. We’ve been through a lot together and I love her deeply. Right now, we’re doing long distance, I live on the central coast, and she’s on the west coast finishing her final year of college and doing an internship. My sister (23F) lives on the east coast. For some added context, my girlfriend and sister actually share the same birthday.

Growing up, my sister and I were always really close. Recently, she went through a really tough breakup and was in a bad emotional space. A week before their birthday, my girlfriend asked if I could fly over to spend it with her, which had been the plan all along. But around the same time, my sister called me and asked if she could fly out and spend her birthday at my apartment. She said she didn’t feel like seeing friends or doing anything big, the only person she wanted to be with was me.

It honestly put me in a really difficult spot. I suggested to my sister that maybe we could do a joint celebration over at my girlfriend’s, but she wasn’t up for socializing. In the end, I told my girlfriend the situation and asked if we could postpone our celebration until next time we saw each other. She seemed disappointed, but she said she understood. I still got her gifts, FaceTimed her on the day, and tried to make her feel loved from afar.

My sister came over and we had a great day, we went to Top Golf, bowling, grabbed dinner, did karaoke night and had fun. It was the first time I’d seen her genuinely happy since the breakup.

The next day, my girlfriend called and told me the truth, that it really hurt not having me there, and even though she knows I love her, it felt like I chose my sister over her. She said she cried on her birthday. I felt terrible, and I told her I never wanted to make her feel that way. But I also told her something I needed her to understand: my sister has been there for me my whole life. She’s only a year older than me, but growing up she was like my best friend. She used her savings as a kid to buy me gifts, cooked for me, took me out when I was down, and never once asked for anything in return. And now, when she was going through one of the lowest points in her life, I just couldn’t abandon her. It didn’t mean I love my girlfriend any less, it just meant someone who had spent years showing up for me needed me to finally show up for her.

AITA?