am I overthinking?

So last weekend I went to a music festival with my husband and best friend. Normally we just drink and dance and have a good time. We don't do any drugs or make the night about that. Just the music and each other.
But the other day, my husband ended up smoking weed from some random person at the rave. And it really upset me.
Normally, I don't care if my friends smoke because it's usually once in a blue moon and I know they're responsible and have their lives together. But with my husband doing it, it gave me a different feeling.
To add some background, he had a pretty crappy lifestyle years ago before I met him. He was a meth addict and did pretty much any other drug you can think of as well. But he's been sober for years and is literally a completely different person. You'd meet him, and never know he did any of that stuff in the past.
So when I saw him smoke the weed out of nowhere, it really triggered something inside me. I know weed isn't that big of a deal. But I think I was just worried that it would tempt him to want to do other things. Not to mention that he took the weed from a random person, and who knows what else it could have been laced with at those types of events.
He noticed I was upset, so we sat down and talked about it for a little bit and he was sorry and he knew it was dumb. He immediately regretted it too because he felt like crap and dizzy after doing it, because he'd been drinking too.
I forgive him. And I know I can't hold it against him too much because I'm sure being in that type of environment doesn't help, and he's back in college finishing his degree with a lot of younger students who smoke and talk about it all the time. So I can see how he would maybe try to justify it in his mind that it was okay to just do it a little bit. 
But I still can't seem to shake that uneasy feeling and I still feel bothered by it. And now I feel like I constantly need to wonder if he's tempted or thinking about doing any drugs again. Am I over reacting? I'm just genuinely worried for his sobriety and well being. And I just want him to continue down the amazing path he's been walking through for a while now. I've just always been proud of him for being the man he is after all he's been through.