I cant handle the anxiety

Okay so throughout my life it hasn’t been easy. My parents went through a nasty divorce because my father had an affair with my nanny who eventually became his girlfriend of 4 years. Then after she left things got better but then it was hell all over again. I was diagnosed with mono in 8th grade and i got really sick and missed my first semester of school pretty much. They found out that I also had Fibromyaliga which is a disease where your joints and bones always hurt and there is no cure except taking tons of pain killers. Throughout this process of going to about 20 million different doctors they also found out I have severe anxiety problems which prevent me from sleeping at night. I was diagnosed with ADHD, OCD, body dismorphic disorder and bipolar disorder. Having these disease I must say makes school impossible for me and my grades are terrible now that I am a freshman in highschool because I missed so much last year and most days I can barely get out of bed.
Also, there was also someone who was there for me and came and visited me in the hospital and kept me feeling sane throughout this past year named Alex. I knew him since we were 11 and he dated two of my close friends. I always had extremely passionate feelings for him but I never said anything. But, over the summer he told me I was the love of his life and that he would take care of me forever if he needed too because seeing me made him stronger inside and we started dating in may. Its now October and we everything is broken. We go to different schools so its hard to see him but on top of that he made varsity soccer and was the 2nd freshman to do it in his over 70 year old schools history. This made him loose it because e has a guaranteed scholarship to any school who needs a soccer player so he left me. He told me that i’m going to be dead or a drop out in 5 years anyway so why should he even care and it made me crazy. I stopped caring about grades and people and just gave up because he made me strong and took care of me. My mother got fibromyaliga after her pregnancy, like me, but ignores me and constantly calls me a failure. She had a 4.0 and skipped a grade and so did my dad and my brother is going to a art school on a scholarship. I’m basically the black sheep of the family and its hard not having alex because I was really close to his mother.
Now i’m here, failing grades, no one who really loves me and diseases that make it impossible to be a normal teenager. I have no where else to turn and I’m done being alone in the world with my suicidal thoughts. I constantly have out of body dreams and I think something is trying to send me a message to go to heaven. I really wanna go to heaven and be with god because I know he loves me no matter what. I just dont know how to kill myself without it being painfull because i want a peacefull death. I’ve told my family and friends that I want to die and i’m going to die young. I know I shouldnt but I have too cause life is too painfull for me. What should I do to not painfully kill myself?