Is it possible to be depress without knowing?

i lost a very close friend (GF) some years back. we dated and so forth. what i didn't know was she was an alcoholic before i met her. but she did say she was an recovered alcoholic. i graduate a year ahead of her and she graduate and went on to KU. she graduated with a Masters in Natral resource. we lost touch along the way. later in years i heard she p away. i was told she went back to drinking and doing drugs. the way she died was so sad. every now and than i cry thinking of her. i ask "WHY?" why didn't u say something, you needed help, support. to this day i still miss her. i never went to her funeral, because its was too late when i was given the bad news of her ping. now i wonder if this is affecting me in some way. i can't sleep, sometimes i just think of her. i never told anyone this story. i wanted to visit her grave. i still have not. what do you think?