My boyfriend want stop weed and we have a baby i need help on what to do ?

i have been with my boyfriend for 2 years now he has done weed ever scenes we met but when i wa pregnant he said he would stop for the baby and now i had the baby who is 3 months now he still has been doing it and he even does in when his sons down stair and he up smoking it i don't know what to do anymore its distorting our relationship i don't what to do anymore please help !