Thank you, masaegu san.
Anyway, regarding the "but ... but ...", most people will not say that, of course. He said that only because he was deeply in thoughts and was wondering if he should leave her alone in the workplace.
All I can think of is something like that (especially when one is suprised or shocked):
Brian: James passed away yesterday.
Kewell: Are you sure? But .... but I just saw him 2 days ago.
P.S. Forgive me for the poor example, my English is not good.