How is a parent to deal with their teen's suicidal ideation?

As a parent, I get conflicting messages. On one hand, it is perhaps developmentally and societally “normal” to think about death/suicide as a teenager. On the other hand, it is dangerous to not take such thoughts seriously.

In addition, teenagers are seeking more autonomy and privacy. Parents can’t expect their teens to be completely open about their experiences, thoughts and feelings.

My teenager has anxiety, ADHD and obsessive-compulsive disorder. He is extremely rigid. He gets called gay and faggot daily in school for the last 5 years. He says he is not gay… which is neither here nor there. He has persistent thoughts about death and suicide. He has thought of many, many different ways to kill himself. He knows his family would be sad and especially thinks of me and his little brother. He won’t take his anxiety medicine because of his rigidity (he has to start on a certain day of the week, at a certain time, swallow the medicine with a certain drink, etc.). He’s not doing homework and is failing two classes. He has been pulled from extracurricular activities and may not be able to go on the band trip, which is extremely important to him (and he plays lead in a few songs that they would be judged on).

I just want to stop the world, but I can’t. I don’t know what to do. He comes home and sits in his room. He only occasionally talks to me, either when he’s doing well or doing very unwell.

Those are my specifics, anyway. How am I to cope, let alone help?