If your uncomfortable, talk to your husband about it. I don't see any signs here to suggest he's having an affair though. I drop my friends to the Airport if they don't have other means of transport occasionally. Maybe the party was just some office thing. Him paying for another girls farewell party? hmmm that one I dunno - was she working under him?

My point is - it's easy to feel suspicious, but no reason to jump to conclusions. And in the end, you should know your husband better than anyone here and should be able to decide for yourself.