Discuss before threesome

I think you should definitely have a discuss before you have threesome. I realized this yesterday after my boyfriend and me having threesome (tinder for couples) with another girl. She was very pretty. We invited her over in my boyfriend’s house. She went in and then we started watching movie. Not long after the movie started, she suddenly started to kiss my boyfriend. So I thought I could join now. I started to touching her body. She slapped my hands right away, saying that she was not ready for it. It turned out that she didn’t like to be roughly touched in her boobs because she just had a plastic surgery.