My bestfriend is dying, i dont know how to cope?

My bestfriend recently told me she's dying or cancer, she hasnt got that long left and i just dont know how i am going to cope when she's gone. she's my only friend tbh so i aways see her. I don't know what to say whenever i see her anymore but i dont want to sound like a tit. i know she's dying and i just cant put into words what i need to say before she goes. Recently shes become weaker and so she cant travel to mine and see me and she's not always well enough for me to go round hers. i really love her to bits and i dont want to let her go.