AITA for not telling my friend that his girlfriend invited me up for coffee and got half-naked in front of me?

Saw my buddy’s girlfriend while driving, offered her a ride home. She said sure, we chatted a bit in the car, all chill. When we got to her place, she invited me up for coffee. Again, I figured it was just friendly (We knew each other before they were a couple)

We’re sitting and talking, then out of nowhere she starts changing clothes right in front of me down to her bra. I got super uncomfortable and told her I had to leave. She got upset, started crying, said she didn’t mean anything weird.

I didn’t tell my friend because I didn’t want to “stir the pot”, but now I feel kinda off about it.

AITA for keeping this to myself?

AITA for not telling my friend that his girlfriend invited me up for coffee and got half-naked in front of me?
byu/Available_Dingo3692 inAmItheAsshole