Which is more important, you and your children, or your boyfriend and his drug habit? Move out, I know you say you love him to bits, but if he loved you the same way back he'd put you and your children before weed.
What is important are you and your babies. Set an example that this is unacceptable (think of it as if your child was grown and was in this situation). I know it will be hard but give him a choice, kick the habit or lose the family. You cant make others change but you have control over your life. Look for help in your community. There are a lot of resources that can give you information about his addiction amd how to help you. You can support him emotionally if he does decide to choose to get help. but remember ypu cannot make him chamge to a man/father he should be.if you have family amd friends use them.you will be able to do it on your own and protect your children. You will set an example to your small but impressionable children how to be strong. Good luck love