If You Could Go Back in Time...

If I could go back, I'd tell you to stop. I didn't know you were doing things you shouldn't have been, I had my suspicions, but I never knew how to ask you about it, fearing if I asked, you wouldn't count me as a friend. And whenever the subject came up, you'd always change the subject so I couldn't ask. It was hard to be your friend for a while because I knew you were hiding something from me, I just wasn't sure what it was. Now I know what it is and we barely talk. What happened?