[ the annoyance isn't something that surprises her. elena merely parts her lips to respond and accepts it - she understands how and why caroline would be.
as to the why... it's a little more complicated. elena's not sure how to explain it - in a way caroline would understand, in a way she hasn't said out loud to anyone but sookie. ]
He thinks it's temporary; that I'm going to go running off to Stefan. [ she lifts her arms slightly. ] That I'll remember, and... He doesn't want to lose us both. [ there's more to it, obviously. she'll get to that soon. ]