My fiancé is using drugs. What can I do?

So. My fiancé and I have been together almost four years. We have one child of our own and he is the daddy for my first two who have an absent real dad.

When we got together he told me he use to be addicted to meth and he had used just about everything else under the son. He told me he moved states to get away from the life and with the help of his brother he got clean and stayed clean. When we met he was five years clean.

Over the last year (since the birth of our child) he has changed as a person. I found out over Christmas he had been going to see a doctor to get adderall to help him focus. I found out when we got a bill from the drs office.

Then he started smoking pot a lot more. Not every now and then. Almost like he was smoking cigs but it was a “vape” thc.

Recently he has lost almost 15 pounds. I’m taking like over two months. Without changing his workout habits. He’s a tow truck operator so his eating habits are too sporadic to track.

Last night we had friends over to hangout and have a few drinks and catch up. The guys were outside and drinking and my best friend and I were inside with all of the kids. Chatting while they are and watched movies and played.

This morning my friend text me to tell me that her husband saw my fiancé using. That my hunch had been right. She doesn’t want me to get them involved because we are all very good friends and knows how serious this can be. She told me where to find everything I’m just waiting for the right time.

But what’s next, I want to support him and help him but honestly I have no idea where to even begin. I’m worried about the kids, our relationship, his health and safety, our families. Any *positive* advice would be much appreciated.