After all, why should he fight it? He likes spending time with both of them, so regardless of which one "gets" him, he has an entertaining time -- and in between, he gets the added entertainment of watching them clash with one another. And by not fighting against either of them and not taking sides, he maintains good relations with both his best friend and his girlfriend rather than alienating them. I think that works out pretty well, under the circumstances. He can't change House or Amber, so he's found the healthiest adaptation to being part of their lives. It would be foolish to jeopardize that out of some sense of macho pride.