why tell her and not me?

okay, so i know i like to spill bout my bf heaps, but now a new situation has arisen!
so me and my bf work together , and today i was working with a girl he obviously talks to alot.
So we're packing this stuff when all of a sudden she says, 'so brian* says he wants to join the airforce?'
i was gobsmacked , didn't knowwhat to say!
i've never heard of him talk about the airforce and now he randomly wants to pack up and leave for like , 9 months???????
wtfff.
why has he told this person he hardly knows and who obviously has a big mouth and he hasn't said anything to me ??
what do i do ,



* = not real name lol.