It's all about attraction, my friend. And the other guy made her feel it. Many of us can relate as this happened to me years ago when I was 16.

If you work on yourself and get confident and don't give a fuck and act bold you won't have this problem. Don't get mad at the girl - women go with their emotions.

There is no easy answer aside from inner-game. If this happened to me now I really wouldn't care because I can find another girl in no time. Work on your inner-game and learn how to be a bold, sexual real man. Be your authentic self and don't filter yourself. You can do all of this while still respecting women and being a good guy.

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This, a thousand times this.
If a girl is interested in you and feels safe with you, she WANTS you to kiss her. If she's meeting you at a group social event, she feels safe.

If a girl is actually meeting me for a date, I have usually kissed her within two minutes. It isn't difficult. It's the closest thing to a "routine" I have. I get her in a good mood, usually by teasing her. Then I stop, take her hand and have her face me(if she isn't), stop talking and look her down, head to toe, and back up, and make strong eye contact. And then I say something about how I hadn't noticed how sexy she looked until now. Then I just step into her and kiss her. I almost never have her pull back or anything else. Best of all, it sets a clear sex tone to the rest of the date.

tldr; Move faster. She wants you to kiss her, and to turn her on while other men aren't able to.

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RSDTyler

Man, I feel for you. I thought she was just someone you picked up on a night out at first.

I've just got back from Spain, was with family for 8 days, then riding solo for 2. I stumbled out my happy hour bar and thought a stroll to the town with the bars and clubs was on the cards.

Anyway's, I got chatting to a group of girls and ended up pulling the hot one. All she kept saying is how she's too old for me as I'm 23 and she was 31. That didn't stop her. Anyways, there was 3 english speaking french guys hitting on the rest of the group and one persistently tried returning to my girl. I'd just casually stroll over at that point and put my arm over her shoulder. We was dancing quite sexually and all the french guy would say is "No, He's gay" This entertained me haha he started getting very drunk and was grabbing her in for a picture and putting his arm around her neck (pretty much choking her). I just gave him the "Wtf you think you are doing stare down" and put my hand out and lead her away from him. I told her then to "Stay away from him" and she did. Later her friends asked here to come here she was just like "no I'm staying away from him"

I wasn't threatened, he was just a creepy overly drunk AFC.
and didn't wanna end up on Costa Del Street Crime on my own

Good luck with next time dude.

This precisely. If she was a girl you've been seeing, and she did that, then 1. You didn't command respect from either the girl or the guy, and 2. She is not someone you should want to be with anyways.

If its just some girl you met on the street and went to a party with, then what happened is completely fair game since she wasn't really yours to begin with, and you got out-maneuvered, or just had a bad night.
Happens to everyone, and not something to beat yourself up over.

The moment some random guy starts talking to a set that I'm navigating, I instantly jump in and be-friend or AMOG him out of the set. When I think about my track record with girls being stolen from me, I don't think it has have happened. You just have to assert yourself. Don't think in terms of controlling the girl's actions but think of it as limiting the guy's actions. Maybe you should have kissed her in front of the guy as he was talking to her. Seems like she would have been down for that.

I was in Vegas with a girl, I left her at a bench as I went to get a drink. When I returned she was being gamed by two other guys. I literally walked up to her and kissed her on the lips and held her. The two guys had nothing to say. They left. She found me way more attractive. Assertiveness is key.

^^^ this! But if she backs off from the kiss, id leave.

I used to have the same problem, I would think a girl liked me, I would think I had good conversations with them, and then they would go hook up with some other guy. Absolutely, kiss her first, but also, if she is flirting and making out with other guys, then you go flirt and make out with other girls. Don't treat her like she's a priority, treat her like she's an OPTION. Flirt, kino, and make out with other girls, she will see that you have OPTIONS, this will make you more pre-selected and she will want you even more.