Problem with relationship or me?..

Hey, I need help from those that are bi or even not bi but have experienced similar things... i have been in a relationship with a guy i really care about for a year now and I am bi, he knows and I realized a few years ago. And while I care about him a lot and see myself having a future with him, I keep imagining myself with women a lot lately... like I'm missing something. I am very confused... I know I love him but I don't know what all of this means. I haven't cheated on him and don't want to sound like an awful person this might be a problem with me.. Please help?..