I need help with my mum!!

Ok so I am 16 and my mother will let me go to the hut with my boyfriend ( we have been dating for over a year and a half) but she won't let me stay over his house or him stay over my house. It's at the point where I am thinking about just not coming home at night and just staying at his place. His mum is over it too and no one understands why she will let me to go the hut with him with no responsible adults around but I can't even stay at his house. What do I do??