I cannot wait until my fiancé and I save up enough to buy our own house!!! We are currently living…

I cannot wait until my fiancé and I save up enough to buy our own house!!! We are currently living at my parents house. My 18 year old brother is into hardcore drugs and has really bad anger. This morning he flipped out because he couldn't find his lighter and blamed me and said I stole it, he then threatened to punch my stomach and ran into the kitchen and grabbed a knife and came at me, thank God my fiancé was there to stop him! I called the cops and I was going to press charges but my mom said she would never talk to me again if I did and if anything happened to him it would be my fault. he graduates High school Friday but he doesn't deserve to walk for graduation.. my mom basically begged his teachers to pass him. I don't want to lose my relationship with my mom , especially with my being pregnant with her first grand child, but I can't take my brother's shit anymore.. its like she's trying to push me away, if she does I will not let her get to know my son. I kind of regret not pressing charges.. she would of just bailed him out of jail and my parents don't have enough money for the bils so I didn't want them to be more in debt.. I don't know of I made the right decision or not.. it has not been a good day.. 😢😢