Masturbating.. help Christians?

my boyfriend alays masturbates and wants me to say sexy things.. but i refuse because its wrong to lust ive used verses and tried to get him to stop but he wont .. its taking over his life, the only thing thats makes him not do it is to say that i will cut myself if he does it bcuz cutting myself is just as a sin and he doesnt want me to do that.. im not gonna actually cut myself but im at a loss and i rea;;y need help i need help fom Christians what can help him stop?