[throwaway_sp11]

I'm just not comfortable with my manager knowing that I'm looking around.

[ornornor]

That’s totally reasonable, you never know how petty your employer can get if they know you’re interviewing.

[freedude]

Perhaps the problem is in the reason you are leaving.

[throwaway_sp11]

I don't understand, why do you say that?

[JohnFen]

People will assume (mostly correctly) that however you've treated past (or are treating current) employers is how you will treat them, too. So it helps to be sure that it's obvious you are treating your current employer professionally and respectfully.