My ex friend started talking with guy I like more, why?

I told my ex friend classmate that I like one guy. We don’t talk much with her now, but she started talking with the guy I like more and more, she usually sits with me, but today she tried to sit with him but there were no place and she sit with me again.
And also when I told her, that I like him and sometimes I jealous when he talks with her, she said like “you can take him, he’s not my type”, but now she acting differently.
I remember when our teacher forced him to sit with me because of assignment, I noticed she was starting at him with smile.
Should I ask her why she’s doing that or I don’t have any right for that?
My ex friend started talking with guy I like more, why?
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