We became a pair of BF and GF recently, at which point we had already been university schoolmates for 2 years.
At the very first few days of acquaintance, during a casual talk about our experiences in high schools, she mentioned that she had had a suspension for 1 year during Senior 1 (US equivalent: Grade 10). Only until recently did I have a chance to ask her about the reason for the suspension, and she replied with a single word: depression. I was instantly shocked upon hearing the response and hugged her tightly.
Fortunately, she didn't have any signs of that in my two years of knowing her, and that night was a really lovely night we had together after all.
What I immediately did afterwards was to Google about "depression" after accompanying her back to her dormitory, so I could have some basic ideas about depression. Many Google results suggested that depression may reinstate under certain circumstances, among which were "triggers", i.e., the same thing that triggered the initial depression happening again, or brought up in memory. (I don't have any experiences with depression - she's the first person around me that I know to have had depression in the past.)
With that in mind, I was very serious about that topic and brought up neither "depression" nor her suspension in any way in the next few days. But I thought I need to know her reason.
The background here is, her status has been pretty well in the past 2 years (her suspension only lasted for a single year and ended 4 years ago) and she's made great progresses in interpersonal relationships, particularly with me. She said she was afraid of love and never believed it a few months back, but not long before she agreed to be my girlfriend. That was an incredible change IMO.
The situation here is, she herself is the only person I could ask about, because it's known that only her family know about this (and not her past schoolmates or friends), while I need to avoid them until necessary. I have no more direct information other than: the suspension lasted for a year; it was because of depression; no one outside her family knows about this (now adding myself as another exception); no more therapy is ongoing (including taking medicine regularly). I have completely no idea about the cause or the severity, and I'd like to know about those.
Long story short, with that in mind that anything unknown could potentially "trigger" the depression (again), how do I safely ask my girlfriend about her past depression, and find out if there was any particular cause?
(I have the feeling that it might be just OK to ask directly, but I have never seen real depression in my life, and I want to err on the side of caution.)