This is what happened: Two guys, me and another one, and one pretty girl. She was quite flirting around with handful of different guys but it was rather obvious that she was with him. She just happened to like me too, for some reason. So when she was flirting with me, I flirted back, just smiled, threw some funny words here and there, blah blah, laugh. He couldn't stand it, he was trying to "protect" her from every guy around. He was constantly trying to tear us apart, stepping between us, pulling her away... I remained nonreactive. I bit my lips and walked away when I saw they are having good time. He eventually flipped out, started telling her things, started getting too anxious, needy, clingy... He injected too much negativity into her - and as a result she dumped him... I won by doing nothing, he lost by doing everything...
Was it easy? Can I say that I didn't care at all? I wish I could say that, but fuck no. It was difficult to remain distant, it was difficult to convince myself and her that I am remaining cool guy, it was very exhausting... I hated that guy too the same way he hated me... But I had a game, he didn't...
So don't be like that guy. Be smarter, have some game. You can't over-react, not in this situation or another. Any excessive reactions shows only your own weakness, dependence, neediness...
The other guy couldn't stand that she was talking/flirting with other guys, right there was his insecurity. He had no game...
Anyway, I know where are you coming from, once you love the girl it is very difficult to be pretending that you don't care, that you are distant... It always sounds easy on a monitor, but reality is different.... There are always other guys who can be good competition, and if we say that the girl likes only one guy (You) it would be a lie... So you have to do something...
There are couple of ways, for example:
NEGATIVE:
* Like the other guy above, you try to take her away. You try to fight. You create confrontation, too much friction till the other guy leaves in one way or another. Another guy is simply your enemy and you will do everything to get rid of him. You need lots of balls for that, you should probably be skilled at fighting too, unless you want to be beaten up all the time and so forth. You are simply a macho guy, but do it only if you have a figure for that, you don't want to look ridiculous either. It's too negative, but you can win some girls like that forever...
POSITIVE:
* Don't be negative towards the other guy. Don't say anything negative about him, rather try to become his friend. Show respect, he is just a guy who like the same girl like you. Shake his hand, smile, say something, and if you have the conversational skills pull her away with something like: Hey, great to talking to you, me and my GF are now going to do XYZ... You got to be sure that she's following you though, otherwise you can lose her (She'll not go with you, she'll stay with him,...). So basically you got to be quite assertive as well. At the same time, make sure that you will (assertively) explain to her that you don't appreciate it, but again, as long as you are magnifying this issue you are also showing insecurity... Also avoid to be Nice Guy, too nice, you don't want to be supplicating, you don't want to show any submissive behavior...
MATURE:
You know the girl, you trust her, you are secure and independent.... You see her talking to some guy(s) - well, you wave at her and go your own way. Let her talk as much as you want. Go talk to your friends or another girls. If there is a good relationship (and in the above example there was), she will come back to you. Don't even bother asking any explanations, you simply ignore it as you are convinced that she is with you. That's probably for couple that know each other longer while, but you can still apply that frame with good results...
COMBINATION of the above:
Simply chose what is working for you. You want to show some maturity, less neediness, more indepenence... You want to have some game. So if she talks to other guys, well, you just bite your lips then, let her talk. If it is too long and too uncomfortable, you show up, try to find out what is going on. Show respect to the other guy, show assertiveness without being negative. She should get your "hint" therefore she will leave with you (assuming that she wants you). If the guy is annoying and refuses to leave, oh well. Does lifting weights ring a bell? It is just another good benefit of lifting, remember, if there are trully not many guys who want to challenge face to face muscle guy that appears rather confident... Be pulite, be respectful, yet don't be a nice guy... Step in his face if needed, and there are no step back, hopefully he will take off without fight. Remember, you have an advantage, she is there with you thus most guys will feel like a third wheel, and there are not so many guys who have guts or balls to keep going after they are confronted)... If she is classy she will join your site right away, meaning he simply has no other choice than walk away... Also make sure that you have a nice assertive talk with your GF afterwards as well. No need to get upset, no need for drama - but she should be clear that this behavior is not acceptable, that you don't really like it. Again, if she really likes you, she will make sure that she will not do it as she respects you...
GO FISHING:
Another good one, probably for more advanced. Ignore (as Franco suggeted). You simply have Abundance Mentality, more choices that you don't have the need to be with one girl. You don't like something that the girls is doing, well, you let her go, dump her. Or, why even bother dumping her, too much effort - you simply go fishing instead, and then you go fishing for another girls. True Alpha? Or just don't care anymore? Be my guest...
Overall, if you follow GC principls you'll get there, once you develop the mindset is is all already included
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Anyway, there are also some other things that might help:
* Create great(er) emotional connection with that girl, which also means good sex. In other words, if the girl loves you she will automatically start dropping the other guys out, and if she does talk to them she will make sure that there is nothing going on. If she truly loves you, there is just no way she will sleep with another guy. You can't seduce woman who is in love with another guy. So if that's the case, who cares if she talks to them? She may tease you just for fun, but she will make it very clear that you are the only guy in her life... You don't want to be protecting a girl much who doesn't care much about you, you'll like a fool...
* Don't show insecurity and neediness. She needs to be free to talk to other guys without you being needy, anxious, suspicious... All this would make you appear weak, bite your lips and have some game
* You should feel confident enough that she is with you, you should trust her enough. Give her the benefits of trust, you can only build great relationship based on trust...
* She should be respecting you, once you are together she should not flirt in front of you with other guys. More classy girls will show you respect by default, they are quite careful to show you respect. At the same time, if you flirt in front of your (classy) girl with another girl, chances are high that she will dump you. She doesn't like that either. On the other hand, there is nothing wrong if she is talking to another guys (or you to another girls), you should be trusting her enough that she will not do anything... Trust your girl brother, and she will trust you back...
* Some girls are more liberal, they just talk even flirt with every guy, yet they can be quite faithful (I believe lots of Puertorican girls are like that, those from the island, not from NY). So if it bothers you find more conservative girl, you will increase the likelihood that she will not fool around...