Birth control help

So me and my bf have been talking about having sex... idk how to ask my mom about getting the shot... my family is really opene about everything, my bf lives with me and he is 19 while i'm 16. i'm sorta afraid they could send him to jail. my dad says they would never do that and my dad knows what were going through since he was 17 when he had my sister. but my mom is real strict i need your advice. please help me