Hmmm, first off it doesnt sound as if you are just fuck buddies? As you stated its a bit more than that. Does she feel the same? Obviously if shes saying that its getting too serious. You can take this one of two ways. Its either a shit test or she generally just doesn't want a relationship and thinks one might happen.

Now from my experience with girls once they have fucked a guy more than once...Then they develop feelings for them one way or another. Otherwise they wouldn't let you fuck them. I've had a few so called 'fuck buddies' which have all failed because the girl has got to attached to me. Men can seperate a fuck from feelings easily. Woman cant.

If you want to keep being friends with benefits then it's going to be very very hard to do so. You can just fuck her...But be her friend as well? I don't think thats possible without both of you developing feelings and jealousy. I mean would you get jealous if you saw her getting off with another guy. Would you get off with a girl knowing she could see? Or would you wait until she wasnt about? Just some things you should think about?