What is everyone's opinion about having a 3some with your partner?

Ariel • Eskimo, German, and Chinese! ✌👑🎮🏊🖤
I want to have a 3some because I am bisexual. But I don't know if I can share my boyfriend with another woman. And I have been told by people that have had 3somes that if I cherish my relationship not do it because it ruins the relationship. :/ Any thoughts anyone?