Dog psychology - any experts in :)

[numtumfutunch]

Our 3y old male (intact) labrador has just spent a week with his tough pal whilst we were on holiday
The other dog belongs to friends, is also a labrador, also intact, also 3y old, also lives with kids but is naturally quite dominant unlike ours

We did the return favour a few months ago and the other hound would pretty well mount anything male within shagging distance, breed or ferocity were no barrier - this dog is seriously tough!
Other dog also lives in the sticks and almost certainly didnt get the socialisation ours did/does and probably doesnt meet any other dogs
He did respect home turf though and the 2 dogs got on absolutely fine as they allegedly did last week

Anyway since we got back at the weekend our normally friendly family wuss-hound has just been bloody moping around looking sad
Hes not engaging with us anything like he used to and just looks depressed

Thoughts are he's cheesed off with us either:

a) as we made him go and stay with the tough dog, even though were assured all was well
b) he would rather have stayed with his pal and is punishing us for bringing him home

Thoughts??