Should I be required to pay 1/2 the utilities when my roommate's boyfriend and dog have moved in to a small 2 bed/1 bath house?

Without any discussion with me, my former roommate’s boyfriend moved in with his dog. Now I have moved out (because of this situation) and the bills are due for utilities. Not only was he there when she was always there, he would show up when I was home alone and she was at work or out. She gave me the amount for the bills—one-half—and I have tried to discuss with her that because he was there, that we should split the bills 3 ways. Even before he ‘unofficially’ moved in, he was there 85% of the time she was there and she did his laundry for him, etc. This is the first time I have mentioned anything about this situation to her. Is it a lost cause?