Is it bad I want to do this

I want to strangle my "best friend" who is dating my actual best friend but I can't tell him how I actually feel about home dating her I'm afraid he will tell me I'm selfish and a prick and stop talking to me and that leading to my real best friend hating me. It keeps me up at night. It's gotten so bad that my real best friend talks to me less and we hang out less I don't want to tell either I've told my real best friend because she's my real best friend I've started to slit my wrists because of this what do I do?