Aw, this behavior is normal and very powerfully driven by hormones - so it's very instinctual for him to do this, and very difficult for him to control until he's neutered. Both of my guys still have their lover dogs - post-neutering - and many (if not most) male dogs do still exhibit some humping afterwards. We let it be since our babies don't ever bother humans about it, just their stuffed lover dogs. Personally, I think they're allowed their dates.
