Mom's live in boyfriend is keeping her hospitalizations a secret but I don't have a POA! Is that legal?

She is frail but not demented. I am her only daughter, and her boyfriend doesn't like me. I've called Adult Protective Services on him before and they opened a case on him, but she chooses him over me. He periodically punishes her by stonewalling and hiding her keys, turning off her computer monitor, not giving her messages. She doesn't care, she is grateful that he is there. I feel like she will die one of these times after a week or so in the hospital and I won't know until after she is dead. He tells her nasty things about me, and she believes him... She is so stupid. I don't want to let him get away with this, but what can I do... she has memory problems due to a stroke, but she isn't demented.