Earning trust back after it's lost

I need to vent my thoughts at the moment. Someone very near and dear to my heart has violated my trust in one specific area. This person is trustworthy in all other areas but one. The situation is complicated by the fact that the issue is one in which deceit has been involved and lies have been told. It involves a substance that is easily abused and an addiction can be formed.

Today, a somewhat suspicious event occurred. I don't know whether I was supposed to see it happen. Probably not. Perhaps it wasn't a big deal. But, I saw the person throw something away in the dumpster, likely unsuspecting that I would be there to see it happen. Was the person throwing away evidence or merely throwing out regular trash? This person isn't usually known for tossing out full trash cans or thinning out clutter. But, perhaps I'm getting suspicious for no substantive reason.

My prayer is that if the person was in fact engaging in deceiving and tossing away evidence of any clandestine activities of the sort I have been speaking, God convicts this person and makes them feel guilty without fail. One of the big lessons I've learned from this situation is that I cannot turn this person from his or her sinful and damaging behavior on my own. I also know that I want to be a rock on which this person can lean for strength, not a threat. As best as I can, I do not want any of my responses to be completely from feeling threatened and angry that the person could continue to do actions that are damaging to those closest to that person. Our Father, our Lord Jesus Christ, guide us through this valley of darkness into your bright light.