strict mom, staying at my bf house

Hi! I want advice, is a big problem if I just tell my mom I will stay at my bf's house for the night, she is really strict and probably will be mad with me. Should I just don't care what she says? I mean I'm not doing anything wrong (I'm 21) and I'm not disrespecting her house rules. But can I be disrespecting her for disobeying her? I live with her.