The rules on content go something like this:
User Content
You agree not to post User Content that:
- Contains any information or content that we deem to be unlawful, harmful, abusive, racially or ethnically offensive, defamatory, infringing, invasive of personal privacy or publicity rights, harassing, humiliating to other people (publicly or otherwise), libelous, threatening, or otherwise objectionable;
- May create a risk of any other loss or damage to any person or property;
- May create a risk of harm, loss, physical or mental injury, emotional distress, death, disability, disfigurement, or physical or mental illness to you, to any other person, or to any animal;
- May constitute or contribute to a crime or tort;
- Contains any information or content that is illegal;
- Contains any information or content that you know is not correct and current; or
- Contains any information or content that you do not have a right to make available under any law or under contractual or fiduciary relationships; or
- Constitutes “Spam”, advertising, or business related communications.
Nothing directly prohibits writing about suicide. However, the rules prohibit encouraging, promoting, and glorifying suicide (which fall under content that presents "risk of harm, death, mental illness"). You will be fine if you put on a mature content tag, a tragedy tag, and clearly spoil the suicide ending in the synopsis. Maybe repeat at the end of every chapter that suicide is never the answer to any problem, and that readers should immediately stop reading and report to their local hospital if they feel they are in danger of harming themself or attempting suicide.
If you commit to writing this story you need to treat the topic of suicide with utmost respect and all the seriousness that the deadly condition deserves.