What to do about relationship issue?

Here's the situation: GF asked me if she could go to a concert... well the concert is in another state, she would be gone for 3 days, and she would be going with a guy she used to see before. She told me it was only about the music and to not worry about him. I kept telling her I was uncomfortable with it. She got mad logged off from chat and refused my phone calls. Wondering if maybe I was being insecure I went to one of my female coworkers wondering if maybe I was just being an idiot and should trust her. I finally was able to speak with my GF and told her I had gotten the same advice that I felt from my coworker. At that point my GF became massively upset with me that I had gone to another woman with our issues. I tried explaining to her I wanted an outside perspective but she feels she can't trust me and that I didn't something that is hugely detrimental to our relationship. I wanted to talk to her but at the time she logged off she was really mad and said she would resent me for it.... I had no idea at that point she had said no at the time. I was looking for a different perspective and now everything is turned and now she's furious with me and feels like I did something wrong. I apologized but she thinks it horrible that I did that. I only want to communicate with her but I was looking to see if I was wrong and my feelings were unjustified and should let her go but now she's mad at me. Any thoughts?