I never would have thought my lover would be upset to hear me say I was on a date with a girl. He and I had discussed the terms and conditions of bringing a girl into our lives. We set some rules: What would one-time vs. ongoing relationship look like? Who makes initial contact? We both walked away from the chat feeling like we understood and were on the same page.
Two weeks later, I told him I was going to get something to eat, not mentioning that I was meeting with a girl for us to get to know better. One of our guidelines had been that I would like to know the person. This is where the miscommunication comes in, he said "me too'. I took that to mean he wanted me to know her. He thought it meant he would. So imagine his surprise! He had at least wanted to know that I was going on a date...before the date. To his credit, I should have told him what I had planned, just a little about the person I was meeting, or at least why I wouldn’t answer my phone for 2 hours. On the other hand, I am a 'don't get your hopes up' kind of girl; I didn't want to tell him until I was sure.
Clarifying the boundaries and complete understanding of the page you are on alleviates the miscommunication. Ask each other questions. Write down the rules. Set up a strategy. These miscommunications are exactly why some people have a bad taste when they hear you are in an open relationship.