Most Helpful Girl
Hmm.. I am more or less in the situation of your gf right now. I just haven't found the right words to leave him. I think, if someone decides to leave a 5 year relationship, this is a very conscious decision. Her saying, that she outgrew you, shows that she internally had already moved on and most probably needed freedom.
I don't think, what you imagine right now, is happening to her. She is not going around with 100s of guys at her feet and she can just pick one and forget about you. A 5 year relationship is a big part of life (esp. at that age) and she will not forget and get over your special connection so soon. I bet she will have moments of loneliness and missing you, perhaps regretting and wondering what if.
But usually a breakup is more hurtful of the person who did the "passive part", because she must have dealt with this situation long before she said those final words.