For songs about people with mental health issues, it's hard to beat the Child ballads. Here are a few suggestions to get you started:

#4 "The Six King's Daughters" - serial murder
#13 "Edward" - varies by version, but all with serious family issues
#75 "Lord Lovel" - narcissism, depression, maybe a hint of suicide
#84 "Barbara Allen" - ditto
#173 "Mary Hamilton" - infanticide
#200 "Gypsy Davy" - adultery, child abandonment
#243 "The House Carpenter" - ditto
#274 "The Drunk Husband" - alcohol abuse
#277 "Dandoo" - domestic violence

Kent