My experience is that it is a bad idea to mix mental health/illness with work. That is, the people that I work for and with should not be intimately aware of my mental health challenges.

They start treating me different - initially it’s a kindness, an accommodation... but it seems over time there grows some resentment and then I have had my mental health thrown at me as “reason” why I can’t be trusted/relied upon or something, with no discussion or warning.

Professional mentor would be different - but I would restrict the content of my discussions with a professional mentor differently than I would my therapist, you know? Also, I don’t think I would seek mentoring from a former classmate.