Friend watched us f*** in a cubicle

I'm 21 and always been very close to my 25yo brother,90% of the time we're together with mates having a good time and my best mate been saying for years we act like a couple and should just f*** and get it over with,when im alone with him i get the feeling something could happen it was just waiting for one of us to make the first move,it eventually did we was out with my best mate and the 3 of us ended up in the toilet cubicle having a sneaky smoke my mate made the comment again and it just happened we had unprotected s** with my mate watching,she won't gossip but he's worried she will.