I am going to disagree with the consensus on this topic...I don't think your girl flirting with another dude is a big deal and I think getting rattled by it and flipping out is a chump move. This is a shit test, nothing more, and if you show her that she hit a sensitive spot you have already lost. This actually happens so often that I have a great formula for it and to be honest I like when a girl tries to pull this because it is an easy way to show her that socially my skills are out of her league and that I can play this game way better then she can:
1) When she begins to flirt with the dude, Do not show even a hint of jealousy. Not even a hint. This is going to be fun.
2) Turn away from her right away provided you can do so without it being awkward or looking unnatural. The vibe is "OK I get that you want to mingle and meet people, so do I".
3) Find nearest woman and chat her up. Preferably introduce yourself to someone new....at a party this should be easy. Kino with an arm touch or something like that as soon as possible. Be laughing and having a good time...hey your ball and chain just gave you an opening to go meet other women.
4) When she comes back, and she will, do not say anything about it. Act like you didn't even notice. She will know that you noticed, she will know that you "won" that exchange and often she will make a non-apology/apology such as "oh my god how come you didn't save me from that conversation" or "hey sorry that dude was a bit chatty"....at which point you will pretend you didn't notice and it wasn't a big deal "no problem, Susan and I were having fun...have you met Susan? <introduce her>"
5) Do this every time and she will stop this behaviour...and if she doesn't then this will be a great opportunity for you that will eventually result in you fucking some of her friends and destroying her social circle. In fact, I have been in situations where girls I was sleeping with were crazy party girls, so I ended up having to do stuff like this a lot, and if it happens a few times with the same crowd and you handle it well it is as inevitable as clockwork that one of her single friends will be like "she is crazy, you are a catch, and you shouldn't stand for that...." <it is on>
1) When she begins to flirt with the dude, Do not show even a hint of jealousy. Not even a hint. This is going to be fun.
2) Turn away from her right away provided you can do so without it being awkward or looking unnatural. The vibe is "OK I get that you want to mingle and meet people, so do I".
3) Find nearest woman and chat her up. Preferably introduce yourself to someone new....at a party this should be easy. Kino with an arm touch or something like that as soon as possible. Be laughing and having a good time...hey your ball and chain just gave you an opening to go meet other women.
4) When she comes back, and she will, do not say anything about it. Act like you didn't even notice. She will know that you noticed, she will know that you "won" that exchange and often she will make a non-apology/apology such as "oh my god how come you didn't save me from that conversation" or "hey sorry that dude was a bit chatty"....at which point you will pretend you didn't notice and it wasn't a big deal "no problem, Susan and I were having fun...have you met Susan? <introduce her>"
5) Do this every time and she will stop this behaviour...and if she doesn't then this will be a great opportunity for you that will eventually result in you fucking some of her friends and destroying her social circle. In fact, I have been in situations where girls I was sleeping with were crazy party girls, so I ended up having to do stuff like this a lot, and if it happens a few times with the same crowd and you handle it well it is as inevitable as clockwork that one of her single friends will be like "she is crazy, you are a catch, and you shouldn't stand for that...." <it is on>