How do I tell my mom I don't like him?

My mom and dad are divorced my dads remarried but my moms not she meant this guy and she really likes him but sometimes when my moms not home he comes over and says if you don't open the door i'm breaking up with your mom so I let him in and hits me and makes a mess then when my mom gets home she thinks it was me and he always does that and I hate him my mom said that in 2 days where gonna go on a 2 week vacation with him and I don't want to go but I still want to make my mom happy so I don't say anything should I tell her?