“Should” is highly personal. Do you really want to have a conversation with them about it? If yes, then yes, you probably should, but you’ll want to be careful about how you approach it. There could be a variety of reasons why they didn’t tell you, and they may be very worried about how you would react to the news. If I were in your shoes, I’d open the conversation with something like, “I want you both to know that no matter what happens, I love you both dearly and you will always be my mom and dad. I’d really like to sit down with you both and find out more about my adoption.”

They might need a little time to gather their thoughts, but as long as you reassure them up front that you aren’t interested in replacing them with your biological parents, it should go well.