Hey there crazyfighter, I'm Jaymc, I'm no mod or arbiter or anything, but I am a 7 year board member and I'm sorry to hear this has happened to you.
Unfortunately the rules regarding this are not well known nor are the easy to find visual access to, but there is a long standing rule against the mention or discussion of suicide, self mutilation, or the intent to do either or for another to participate in either.
This was a change about 4 years back, a carry over from an in game change where riot took a stance against the mention of such negative and devisive topics among the community.
I'm truly sorry to hear you were suspended out of ignorance, but there is indeed a universal board rule regarding that specific topic subset and it is banned on all sub boards.
Hopefully you can hop on the moderator discord and explain this to them in person. Just head over to GD subboard for the particulars on how to speak with some on on the staff in person in a timely fashion. That should get you sorted out and hopefully just a minor time out or maybe just a warning.
(Also @ mods, sorry for discussing the topic, figured it could use clarification)