AITA for skipping my brother’s wedding because my girlfriend wasn’t invited?

My brother Mark (31M) and I (29M) have always been close. I was his best man at his engagement party. I helped him move twice. When he proposed to his fiancée Kayla, I was the first person he called.

I’ve been with my girlfriend Jess (28F) for four years. We live together, we split everything, and she’s been to every family holiday since our first year. My parents adore her. Mark has called her his “honorary sister” more than once.

Three months ago the wedding invitations went out. Mine came in the mail addressed to me alone. No “and guest,” nothing for Jess.

I figured it was a mistake and texted Mark. He called me back, sounding awkward, and explained that Kayla had set a strict “family only” rule because of budget. The venue charges per head, and they had to cut the guest list hard. Jess, he said, would “totally understand.”

I said that was fair, and asked who else was on the list. That’s where it got weird.

Kayla’s college roommate of six years is bringing her boyfriend of seven months. Two of Mark’s coworkers have plus-ones. A cousin I barely know is bringing someone she started dating in the spring. Jess, who has been to Mark’s birthday dinners, his housewarming, and every Christmas for four years, is the only long-term partner not invited.

I asked Mark about it. He said Kayla “doesn’t know Jess that well” and that it “isn’t personal.” I said it felt pretty personal when strangers’ boyfriends got seats and my girlfriend of four years didn’t.

He told me I was overreacting and that I should just come alone “for one night.”

I thought about it for a few days. Jess told me, honestly, that she wasn’t going to be upset if I went without her. But I could tell it hurt her, and it hurt me too. So I told Mark I wouldn’t be attending unless Jess was welcome. I wasn’t angry. I said I loved him and would celebrate with them any other way: a dinner, a gift, whatever they wanted.

That’s when it exploded.

Kayla texted me that I was “holding her wedding hostage.” My mom called crying, saying I was “choosing a girlfriend over my own brother” and that I’d regret it. My dad said I was being stubborn about a single evening. Mark hasn’t spoken to me in two weeks except to say I was “ruining the best day of his life.”

A few relatives sided with me and said it was disrespectful to exclude Jess. Others said weddings are the couple’s day and I should respect their rules, even if they’re unfair.

The wedding is in three weeks, and I still haven’t decided whether to go. Part of me thinks I’m being petty. Part of me can’t shake the feeling that if the situation were reversed, Mark wouldn’t go without Kayla either.

So, AITA for skipping my brother’s wedding because my girlfriend wasn’t invited?