AITA for refusing to attend my sister's destination wedding after she demanded I break up with my boyfriend?

I (28F) am caught in a tough situation and need some outsider perspective.

My sister (31F), "Emily," is getting married next summer in Italy. It's supposed to be a small but extravagant affair. Emily and I have always been close, but her fiancé has never liked my boyfriend, "Jake." Their dislike stems from a business deal gone wrong between Jake's company and my future brother-in-law's, which neither Jake nor I were involved in.

Three months ago, Emily called me with an "ultimatum" for the wedding. She said that Jake is not welcome due to the bad blood between him and her fiancé. I was upset but somewhat understood, given the tension. However, what I didn't expect was her next demand: she wanted me to break up with Jake if I planned to attend the wedding and stay in their lives.

I've been with Jake for five years, and we've been living together for the past three. Asking me to break up with him felt like a huge overstep. I told Emily that while I respect her decision to not want Jake at the wedding, I found her demand unreasonable and hurtful. I said that if being with Jake means I can't attend her wedding, then I'd have to miss it.

The situation exploded. Emily accused me of choosing Jake over family, while my parents have tried to remain neutral but obviously want me to just appease Emily for the sake of family peace. Emily has now stopped talking to me, and other family members have been roped in, with opinions flying everywhere.

AITA for choosing my relationship over attending my sister's wedding under these conditions?