To me - and this is just me and nobody else - it seems selfish to be unwilling to be happy for a partner when they've had a happy-making date.

I know from personal experience that this is not usually the case with Brian. Yes, he has jealous patches, and he's working on them, but I have certainly seen him be happy when partners have had had good experiences with their OSOs. Whether he communicates that to his SOs is a different matter, and one which I am not privy to.