The Big Question About My Flirtatious Games

Hi everyone, this is going to be a long one, so bear with me. I'm in a relationship of five years, and things have always been great... until recently. It started when my partner suggested we try some little play, it was fun at first, but lately, I’ve found myself wanting to push the boundaries more than ever. Yesterday, he came home from work frustrated about something that happened with his manager (who’s in her early thirties). She’s been flirting with him for months now, and while they're just friends, it's clear she sees him as much younger and more naive. This brought out a side of me I didn’t expect, I wanted to protect him from this woman and somehow take care of the emotional mess left behind by her advances. The funny thing is, when I acted like his protective big brother during dinner last night (which was very different from our usual dynamic), my partner seemed genuinely comforted. But now here’s where I need help: Is it normal for me to feel this way? Should I be worried about these impulses? It feels healthy in one sense but also intrusive and confusing at the same time. Thoughts?