AITA for Catching My Boyfriend Sleeping Behind a Locked Hotel Door During My Promotion Party?

I (28F) have been with my boyfriend (31M) for almost five years and everything looked perfect until the night of my promotion party when I started noticing strange behavior between him and his coworker (27F), who someone I trusted because she used to be my friend from college. My best friend (29F) came with me to the hotel venue, and my brother (25M) was also there helping set up the event, so I wasn’t alone that night. Throughout the evening I kept catching them exchanging looks, and my boyfriend kept disappearing at the same time she did, always claiming work emergencies or urgent calls. I tried to ignore it until my brother quietly told me he saw them together in the service hallway earlier acting too close for comfort. My best friend suggested I stay calm and wait until after the party ended, but something in my gut felt wrong and I couldn’t focus on anything else. When I checked the private lounge area to find him, I froze seeing them inside a closed room, and my phone rang while I stood there hearing his voice say don’t open the door yet.

For a moment I honestly thought I misheard him.

Because why would my boyfriend be inside a locked lounge room at my own promotion party telling me not to open the door? My hand stayed frozen on the handle while my phone kept ringing nonstop—my best friend outside probably realizing something was wrong. My brother walked up behind me and whispered, “Open it.”

I did.

The door didn’t even fully swing open before I saw them clearly.

My boyfriend (31M) was sitting on the couch fully dressed but looking panicked, and his coworker (27F) was right beside him adjusting her hair like she had been caught in something she couldn’t explain away. The room itself had drinks, jackets, and his phone face down like he had been hiding notifications.

The silence that followed was so loud it felt unreal.

My best friend (29F) came in right after me and immediately said, “You told her you were working late for THIS?” My boyfriend jumped up instantly, saying it wasn’t what it looked like and that they were just “talking about a work emergency privately because the party was too loud.”

My brother actually laughed at that.

Because he had literally seen them together earlier in the service hallway, and now they were locked in a private room at my event.

Then the worst part happened.

My coworker friend—yes, the same girl I had once helped get hired years ago—finally spoke up. She said she “didn’t want drama” but that they had been “emotionally close” for weeks and that nothing physical had happened, just “confusing boundaries.”

That word—boundaries—made me snap.

I asked my boyfriend how many “boundaries” require a locked door at my own promotion party while I’m outside celebrating a job I worked years for.

He didn’t answer.

Instead, he tried to grab my arm and pull me aside, saying I was embarrassing him in front of people. That’s when my best friend stepped between us and told him not to touch me again.

My brother had already started recording because he said he didn’t trust how quickly things were escalating.

And then guests started noticing.

Someone from HR at my company actually walked past the hallway, saw the commotion, and came inside asking what was going on. That’s when my boyfriend completely changed tone and tried to act calm, saying it was a “misunderstanding between colleagues.”

But the coworker broke down crying and said she didn’t want to lie anymore.

She admitted they had been meeting outside work, including during times he told me he was “stuck in overtime,” and that tonight wasn’t the first time they had been alone together at an event I was attending.

That hit me harder than anything else.

Because it meant this wasn’t a mistake that started tonight.

It was planned.

At my promotion party.

I told him to leave immediately. He refused at first, saying it was his “plus-one invitation too” because I had once casually added him when I booked the venue. My brother stepped in and told him if he didn’t leave, security would be involved.

That’s when he finally left, but not quietly—he kept saying I was humiliating him and ruining his reputation.

After he left, the entire night collapsed.

My promotion speech never even happened. My boss later told me I looked “distracted and shaken,” and I had to explain everything the next day.

My coworker friend was suspended pending investigation after HR confirmed she had crossed professional boundaries multiple times. She tried to message me later saying she “never meant to hurt me” and that I “overreacted by exposing everything publicly.”

My boyfriend has now been telling mutual friends that I set him up by inviting him and then ambushing him in front of people instead of handling it privately.

Some people say I should have waited until after the party so I wouldn’t ruin my own celebration. Others say I was already being disrespected in my own event and had every right to open that door the moment I did.

Now I’m stuck replaying it.

So… AITA for opening that door and exposing everything in front of everyone instead of dealing with it privately?