AITA for canceling my wedding after catching my fiancé practicing his vows with my sister?

I (28F) was supposed to get married three months ago to my fiancé “Ryan” (31M). We had been together for five years, engaged for one, and honestly everyone around us thought we were the perfect couple. He was charming, successful, close with my family, and especially close with my younger sister “Lily” (25F).

And before anyone jumps to conclusions — no, I never thought anything inappropriate was happening between them.

Lily has always been bubbly and outgoing. Ryan was naturally friendly. They joked around a lot, teased each other constantly, and had the kind of sibling dynamic that honestly made me happy because my past boyfriends never got along with my family.

If anything, I thought I was lucky.

About two months before the wedding, Ryan started acting stressed. He became weirdly distant, constantly distracted, and spent a lot of time on his phone. Whenever I asked what was wrong, he blamed work pressure and wedding planning. I believed him because planning a wedding is stressful.

Then little things started bothering me.

One night I came home early from work and found Lily at our apartment even though Ryan never told me she was coming over. The second I walked in, the room went awkwardly silent. Ryan immediately stood up and started rambling about how Lily was “helping with surprise wedding stuff.”

Another time I noticed they suddenly stopped texting when I entered the room.

Again, I ignored it because I trusted both of them completely.

The week before the wedding, my friends threw me a bachelorette dinner. Ryan said he’d stay home with some friends and work on final wedding details. I got back around midnight exhausted and slightly tipsy. When I walked into the apartment, the lights were mostly off except for the living room.

At first I thought Ryan was on the phone.

Then I heard him say:

“You’re the only person I can picture when I say these vows.”

I froze.

My heart literally stopped.

I slowly walked closer to the living room and saw Ryan standing there holding papers in his hand while Lily sat on the couch crying.

CRYING.

He looked up, saw me standing there, and immediately went pale.

I remember laughing because my brain genuinely could not process what I was seeing. I kept waiting for someone to explain the joke.

Instead, Lily stood up and started saying,
“It’s not what you think—”

Which, honestly, is probably the worst sentence a person can say in that situation.

I asked Ryan why he was practicing romantic wedding vows with MY sister at midnight while she cried on our couch.

And this man actually had the audacity to say:
“I didn’t want you finding out like this.”

Finding out WHAT?

That’s when Lily burst into tears and admitted they had feelings for each other.

Apparently it “just happened” over the past year while helping plan the wedding together.

I felt physically sick.

Ryan started crying too, saying he loved me but also loved her and had been “confused for months.” He claimed they never technically cheated physically, but admitted they’d been secretly meeting up, texting constantly, and emotionally falling for each other behind my back.

While I was planning our wedding.

I asked Lily how long this had been going on, and she admitted it started after a family vacation last summer. Meaning they spent almost an entire YEAR smiling in my face while hiding this from me.

The worst part?

My parents apparently already suspected something.

Not enough to tell me, though.

My mom later admitted she noticed “tension” between them months ago but thought it would fade. My dad said he didn’t want to accuse anyone unfairly before the wedding.

So basically everyone watched me walk toward humiliation in real time.

I didn’t scream. I didn’t throw things. Honestly I think I was too shocked to even cry.

I just quietly took my engagement ring off and placed it on the kitchen counter.

Then I looked at my sister and said:
“You didn’t just steal my fiancé. You destroyed our family.”

And I walked out.

The next morning I canceled the wedding entirely.

We lost thousands of dollars in deposits. Family members were furious. Guests had already booked flights and hotels. Ryan’s family blamed me for “acting impulsively” instead of trying therapy first because according to them, “nothing physical happened.”

But honestly? Emotional betrayal hurts just as much.

Things got even worse when Ryan and Lily officially started dating TWO WEEKS after the canceled wedding.

So clearly they figured out their feelings pretty quickly after all.

Now my family is divided. Some relatives think I overreacted because technically there was no affair. Others completely cut Lily off for betraying me. My mom keeps begging me to forgive my sister because “family is forever.”

But every time I think about them together behind my back while helping me choose wedding flowers and venues, I feel sick all over again.

So… AITA for canceling the wedding and cutting both of them out of my life completely?