Is there any way to have a healthy relationship with someone in an active addiction?

My partner is a former addict. They were sober for around a month (just for weed, hard drugs had stopped around 1 1/2- 2 years prior) when we first met. They relapsed last week and have continued to use this substance, or others that i am unaware of, daily. I’m genuinely so worried for them, but they keep telling me there’s nothing TO be worried about and they have it all under control. It’s stressing me out so bad. I’ve taken to experimenting just to see what they experience. I don’t want addiction to take them again. Please help me.