If I was seeing a therapist for addiction and therapist made sexual advances, can I sue even if it happened 3 years ago?

You might be able to sue under medical malpractice or similar type theories of law involving special relationships but do not sit on it. The longer you wait the shorter your time period may be to sue. Further, the longer you wait, the worse it can be for you in court or arbitration in that the judge, arbitrator or jury may think your motives are less than truthful and therefore may not believe you. You need to write down as much as you can remember from when it happened, how it occurred (the more detail you can remember the better) and how you wind up leaving this therapist. If you filed a complaint with the state licnsing board, this will help your case, as well.