So it IS something stupid and childish. I should've guessed as much. Don't know why I tricked myself into thinking it was actually important.
There's no problem here. Your brother is happy enough banging a pretty blonde, I'd wager, so unless you're jealous of either one there's no problem. If it IS jealousy, then you're either a lesbian or a brother-fucker.
Thank you for telling me this, it's...deeply amusing.