He's love is unconditional, and although he is physically very strong, he doesn't have the mental strength to fight with his love, feelings and passion. He has never encountered this before as Bella is different from anyone Edward has ever come across. He longs to be with her but his unselfishness is too over powering which therefore means he tells her he can not be with her.
'Girl save your soul' He wants her to leave him because he doesn't have the power to.
This book is amazing. I recommend it to virtually anyone!
'About three things I was absolutely positive. First, Edward was a vampire. Second, there was a part of him, and I didn't know how dominate that part might be, that thirsted for my blood. And third, I was unconditionally and irrevocably in love with him. '