How do I control my homicidal and suicidal feelings?

So for a very long time I have had mental issues not huge but still quite negative. It started with mild depression following a suicide attempt when I was eight years old and that's when things began to change inside my head, as the years went on it began feeling as though I had two people crammed into the same head because when I was younger I was really kind and calm but I soon became extremely violent, yet I never stopped being kind and calm it just varied at the times, seemingly the calm quiet kind part of me is fading away and though I am very composed and am not physically violent I feel very cut off from people and I want to kill them and myself. Because of my disorder (most likely schizotypal personality disorder (my therapist suggested this after thinking I was a schizophrenic but realizing I may not be due to lack of hallucinations. )) I have a hard time making friends but I have one friend outside of school and two in school. My friend outside of school has been my friend for 3 years and usually after I talk to him for a bit my violence goes away for a while (most likely because I feel that "human connection") yet after visiting him the entire day I feel no better and I fear that soon even he won't keep me from snapping into a crazy/violent tangent. Before someone suggests "get help or tell your therapist " Im not going to, I can't, if I tell her I am homicidal and/or suicidal she will lock me up and never let me out. How do I keep myself from doing something stupid or violent?