Consequences & that actions have them.

Yes it might have been something relatively minor but he betrayed your trust, he lied to you.

He needs to learn that trust is something that is easily lost and takes a lot to earn back.

I know I did some things in my youth that lost the trust of my parents and it took a long time to earn that trust back, I paid for it in a big way. Once I'd earned the trust back and showed that I was responsible, I had a lot more freedom. I ended up being able to do things that had other parents shaking their heads, I even had school friends comment at our reunion a couple of weeks ago that they were amazed at what I was able to do when we were at highschool, but it was because I screwed up and had to fight to prove I was capable and mature enough to behave and not lie.

Good luck