Not sure if I'm down but I'm curious

Last night I was with a dude messing around and his phone kept going off and while I'm giving head he brings up a three some. So I know it was a girl trying to get it in with him.

I didn't tell him no but I didn't say yes either. I don't know if doing that will shake up my self confidence and I'm not trying to feel like shit lol but at the same I've always been curious what a threesome is like. Although I am a little scared of catching an STD.

So the whole thing was left up in the air so one day I'm expecting he's gonna bring it up.

Anyone out there had a threesome before?