Sexual harassment??

Ok so my moms boyfriend is 39 years old I’m 17 about to be 18 in September. Her bag has been sending me messages like this for the past month. My mom was notified when it first began and hasn’t done anything about it because she thinks it isn’t harassment. I no longer feel comfortable around my house or around him. If I were to report this to the police would they consider it sexual harassment or would they do nothing about it? I want to report it and get a restraining order but I want to do it without my mom finding out about it because she’s on his side and I’m not sure what to do?...any advice?

Update: I am getting a restating order to where he is not allowed to be around me. To where either I have to leave when he comes to my house or my mom has to go to his house. And I have talked to the cops. Thanks for the help everyone!

Update: I have a restraining order he is not allowed to be in the same facility as I am. I am not able to move out of my moms due to me still being in school. I have a year of high school left and I am moving out. I have told other family member so they are all on my side. My mother is starting to come around to being on my side. Thank you all for the support.