I don't know why my stepdad touches me

My stepdad grabs my butt and sometimes rubs my thighs i tell him to stop he doesnt he also grabs my stomach and puts me close to him i push him away and i tell him to stop and he just gets more violent and I just hate it one incident I was in the shower and he needs to use the bathroom so I say fine come in I did get a gut feeling that something was gonna go wrong once I said that so im just washing my hair then he just opens the curtain and says surprise! And keep in mind that im 14! I keep on blaming myself for that incident. I tell him to get out and im trying to close the curtain but he's still trying to open it he says oh im sorry I didn't mean to do that and I just tell him get out you freaking pervert! After i get out of the shower I went out and he's still apologising and he put a knife to his chest. I say it's okay but it's really not. 1 month later he's still touching me. Also while I sleep he kisses me on the lips and I feel discusting im always crying. Sometimes I think im just being a little crybaby and other people have it worse. And I don't know if I should tell my mom. Mom and him already dont have a good relationship my mom wants to leave him so should I wait to tell her right now or later in just scared for my little sister's and mom and I im sorry if this was all over the place. I just don't know what to do.