Relationship

My girlfriend and I have been together for 11 moths, already going on 1 year. She has recently made 2 new friends at school. About a month ago she decided to try out a polyamorous relationship. She asked me if I was okay with it. Clearly I wasn't. But I didn't want to try to seem boring. This polyamory thing only lasted for 3 days. It was torture. I felt like I couldn't talk to her about things anymore. Everything seems a bit better but the things that happened, skarred me. I love her. And that's all that matters.