What does my girlfriend mean by this?

We recently became engaged and I do love her but I don't understand what she's trying to say.

We were at the mall and stopped to sit down and eat. She saw me staring at a woman walking past us. She nudged me and smirked "How does it feel knowing that you can never f*ck another woman again?" and she turned around to continue eating her food.

What does this mean?

Self explanatory: look but dont touch!

Would you ever say something like that to her? Think about that and you might have your answer.

I would have responded - ''Hmmm maybe it's time to tell you about my harem. '' (said with a smirk) or just ignored it and laughed at her.

I probably would have responded with "not without protection, that's for sure..."