Reddit, is my girlfriend tricking me?

I have been dating this girl for around 8 months now. We are both 17 and have had sex with each other. She was my first, but I was not her first, however. Today she told me when I go on vacation next week, if I meet a "hot beach babe" I could have sex with her. She said she wouldn't get mad, she wouldn't want to have sex with another guy, so I don't know why she would let me do this. She's also open to a FFM threesome (female, female, male). So, is she tricking me somehow?

EDIT: On a side note, I just finished How I Met Your Mother, what show can I watch now? I hate The Big Bang Theory.