I'm not sure about that. I think at this point he's just... resigned to losing people after what happened in the Time War (which he spent series 1 and 2 being pretty affected by!)
I'm glad you're enjoying 4, though- it's one the weaker series, I think, so it's all uphill (well, mostly) from here.
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"Biting is excellent- it's like kissing only there's a winner."