What do I think 🍁

My bf has last night tried out weed and is considering doing it every now and then, I'm not against It and don't have a problem with him trying it but I feel uncomfortable if it's going to occur every now and then. He won't listen to me and is just telling me to chill as I'm also asking if it'll change anything like either out relationship or him. He simply replying it'll be fine , however I'm worried. What can I do? I don't want it to change anything or be a regular thing.