AITJ for not telling my ex’s fiancée who I was the moment I realized it was his engagement party?

This happened Saturday and I genuinely cannot stop thinking about it.

Some background. Jake and I dated for two and a half years. Broke up fourteen months ago. It was mutual but it was hard. We don’t follow each other on anything and we don’t have a lot of overlapping friends anymore. I had genuinely moved on. No bitterness. No late night texting. Nothing.

So Saturday. My coworker Priya invites me last minute to a dinner thing at a restaurant downtown. Her friend is celebrating something, she says. Come it’ll be fun she says. I almost said no because I’d already changed into my pajamas.

I went. I should have stayed in my pajamas.

I walk in and it takes me maybe thirty seconds to see Jake standing by the bar.

My stomach just dropped.

I grabbed Priya’s arm and whispered why is my ex here and she went pale. She had no idea Jake was connected to any of this. She knew the fiancée through a completely different circle. Nobody had connected the dots.

I should have left right then. I know that now.

But before I could move his fiancée came over and introduced herself and she was so warm and so genuinely happy and I just froze. I smiled. I shook her hand. I told her congratulations.

I stayed for maybe twenty minutes before I quietly told Priya I needed to go.

Jake saw me leaving and followed me outside. Asked me what I was doing there. I explained. He didn’t fully believe me. Said it was “a weird coincidence” in a tone that meant he didn’t think it was a coincidence at all.

I went home. Cried a little if I’m being honest. Not because of him. Just because the whole thing was so incredibly uncomfortable.

The next day Priya told me Jake’s fiancée had been asking questions about who I was and how I knew Priya.

I don’t know if I should reach out and explain myself or just leave it alone.

My sister says I did nothing wrong but also maybe should have left sooner. My friend thinks I should message the fiancée directly.

I just want to know if staying those twenty minutes makes me a jerk.

AITJ?