God… Why does this keep happening :(

I love this girl and we recently got together and she loved me as much as I loved her, but a week ago she tells me to go to here house. Alone, So I did and she told me that she wanted a “Open Relationship” where she can go explore the world but still have me in her life.. It makes me feel kind of used but I don’t know I want to keep it the same, she still kisses me and stuff… but she told me the other day that she liked this guy…. and I almost lost it, like 2 days after we, like half broke up she told me she liked this guy?!?! like wow.. she told me just the other day that he didn’t like her back so that made me happy, but she said she loved me just the other day and now she is moving on?!?!?! What do I do? 🙁