Does committing suicide always lead to damnation?

I attend a Catholic high school and this topic was brought up during health class. The teacher claimed that it is not always a mortal sin as some people have mental illnesses. This didn’t sit well with me as the taking of a human life is a grave matter, one has full knowledge, and one knows it is wrong at some level. Even with mental illness all of these things remain true at some level. I do not believe we would justify murder as not being a mortal sin if one is a psychopath, even though the mental illness may be the primary reason. I understand we never know what God will do and that he could theoretically forgive a mortal sin without confession, but we cannot ever know this, so I find it odd to use that as a reason. No, I am not suicidal, I am in a great place, this was just a question I cannot get out of my mind.