Broken relationship (help needed asap)

My boyfriend and I have been together for 2 years, and all he does is constantly disrespect me, belittle me, stress me out, mentally and emotionally abuses me. I'm 17 and I'm in my junior year of highschool and he graduated last year. I'm not happy and I already know what the answer is; it's gonna be leave him alone. Easier said then done… He was my first kiss and I lost my virginity to him, but he's cheated and lied to me and I always stayed until his friend came into the picture and treated me like a queen. He's never disrespected me or called me out my name and I'm happy with him but if my current boyfriend finds out I'm talking to him again he promised he's gonna take my life and his"exfriends" too. Please I need help to get out this relationship, I'm no longer happy and all the constant abuse gave me severe depression and anxiety. I wanna be able to pass this dark part of my life but the only way I can is if I leave him. I love him but I just can't do this anymore.