What does it mean when your girlfriend says that she wants to breakup with you because the relationship is going to fast and it might be better if you stay friends but you have strong feelings for her?

If she says that the relationship is going too fast and that she just wants to be friends...well there really isn't much to it. You may have strong feelings for her, but it's not that way for her. She sees you as too good of a friend to be intimate with, and that it would be awkward to go any further, which you might have been trying to, as implied by "relationship is going too fast". But then again, maybe she's just having a moment in the relationship where she questions it. the best thing to do is not to anger her in anyway. Respect her descision, whatever it may be.