What happened with this girl? She was all over me then went cold?

I met a girl on holiday she seemed into me we ended up hanging around a lot day and night for 3 days. During this time i met another guy as was travelling. I introduced him to her. For what its worth he was better looking and more social than me. At first all 3 of us were having fun open conversations drinking etc. Then over next day they got closer and by next day despite us all hanging together as we went on a trip i had become invsibile. She would be chatting with him sex and private things talking dating stuff like as if i wasn't even there. Before he came along this was like me and her now it was him taking my place. So i guess she preffered him but how can she go from 10 to 0 on me just like as if the previous days never happened.

What happened with this girl? She was all over me then went cold?
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