You have chosen to become sober for yourself - as you said, you
You can have a short, calm conversation with him - maybe at a good time of day, if you prefer (your choice) - and make that clear. You still care about him, but you also care about yourself - which you should - and you need to do this.
Then - you do it.
There’s lots of good resources, including podcasts, books, and recovery groups, here:
This will be a learning curve for you as you get started on the road to recovery. It will not happen overnight and you have to take it one day at a time, don’t get overwhelmed. Be gentle with yourself and if it helps you cab remember this simple rule: you are allowed to do anything that’s safe and legal, to stay sober. Eat pizza three days in a row? Ok. Binge watch a Netflix show? Fine. Walk for hours listening to podcasts and music? Fine.
It’s all good, as long as it’s safe, legal, and sober. The emotions will be up and down and occasionally you will get thoughts of using. They will pass. Say to yourself, “I am having a thought of using.” See it, acknowledge it. It will pass. They all eventually do.
Do that one day at a time, and work your recovery daily, and you will get there.