Can someone really fall in love with someone in 4 months?

my girlfriend tells me she loves me and I feel the sincerity behind it however, it seems soon, its so easy for her to tell me shes in love with me, and shell wait for me to say it, and Im not sure im on the same page as Im not in love with her, as I explained shes admitted this to me, and its kinda a weird position to be in as I dont want to crush her however I know I dont feel the same way quite yet