Threesome will change your relationship

Relationship will be different if you had a threesome with your partner. I had a threesome hookup with my girlfriend and it turned out well, but it did changed our relationship. We used to be in a monogamous relationship, but now, everytime I heard her talk about another women or men, instead of being suspicious, I would think if she is going to invite them over to hang out. By saying hang out, I mean having a threesome dating.