What do I do if I found out that my gf is still in love with her ex?

She told me that she didnt love him anymore, and I didnt like him because of some stuff that we had gotten into. So i asked her if she dont speak to him no more... and that its either him or me. She said ok. Now we are 5 months into the relationship and i got someone spillin all the beans about her.. so my gf admitted to still being in love with him 3 months in the relationship and that she lied about when she said she had stopped talkin to him. But now shes tellin me that she dont love him no more. but my thing is that i dont trust her now, but i love her. what should I do? and she's all "ok i lied, now get over it" what should i do any answer thanks