Hey everyone, haven;t been on in a while, i hope everyone is doing well

Had a quick question, if you had a friend who couldn't tell you what was going on with them a few yrs ago , but could now, Not sure what they struggle with, maybe bipolar disorder( which im educating myself on) If they decide to tell me, Do I say I know to make the admission easier for them, or do i act like i dont know , just listen?? What is the correct thing to do??