My gf got hit on and I kind of liked it

Over the course of the 2 years we have been together she’s been hit on a fair amount and every time if I’m there I get mad. This time tho for whatever reason there was no anger I just honestly liked it and idk why I feel like this. We were out with some of our friends and were getting ready to leave so I was saying goodbye to a couple people and some dude came up to her. I didn’t see at first but then I walked over and he walked away and she told me what happened obviously he was just a drunk idiot. He was super flirty and grabbed her arm. Instead of going over to confront him and be all angry though I liked it I didn’t tell my gf I liked I just pretended to be mad. So yeah these are all very new feelings no idea why I feel this way so here I am sharing. Anyone else ever experience something like this?