toy poodle not adapting to live-in boyfriend

[kamouraska]

I have a two year old toy poodle who was well behaved and has gone through two obedience schools, but since my boyfriend moved in a month ago, she's reverted to peeing on the floor, barking more often and actually bit someone for the first time. (a gas station attendant who put his hand into our car to pet her). I'm not sure how to help her adapt and much of this behaviour seems new. She's very smart, learns quickly and is usually a very pleasant dog. But lately she's seemed more stubborn than usual. Does anyone have any tips on how I can help her to adapt to this new situation? We've bought a gentle leader and we've been told that we need to re-assert our dominance. Any concrete tips on how to do that?