Exploring Boundaries in My Open Relationship...

So I'm in my first year at law school and also in an open relationship with Rachel. It's been a great way to explore different types of connections while maintaining the depth of what we have together. Last week, though, something happened that made me question if we were setting healthy boundaries. One night, I went out with Sarah, whom I met through a group activity...and it wasn't just friendly chatting. We ended up at her place and things got...intense. Not graphic here, but let's just say it was more than a casual meet-up. When I told Rachel about it the next day, she seemed understanding...but also kind of distant. She didn't bring it up again until weeks later, when we were out with friends and suddenly she started asking me pointed questions about my night with Sarah that seemed like probing for details. It felt weirdly uncomfortable and awkward. Is this normal behavior in an open relationship? Should I have handled it differently...or should Rachel be more open to my choices without pressing so much later on? What do you think...