I think for most sensitive girls (I would say I am one) I think it is best done like a band-aid - really. A lot of the time we fake that we are sensitive and vulnerable so guys feel they can't leave us. Also, how do you know that she doesnt doubt the relationship as well. Above all - you need to tell her how you feel. I can guarentee that is the only way to go forward. And when you tell her, just say 'we need to talk about us' so she knows exactly what is coming.