Social services will get involved if they think you aren’t protecting your children. My honest opinion is have him removed or go somewhere to a family members.
They have to see you are putting your kids first and not in a dangerous situation with someone who’s vulnerable.
If they think your children are in danger them will remove them and trust me I know because I seen it happen with a few people at the drug service I go too.
If you tell them you want help to get him gone they will help you….
Listen while am giving you advice sorry to be blunt but my ex would of done the same to me. Your children will always come first and there safety is your job as a parent. Difference with me was I never went back or had my children when I was off my face. Doesn’t make me any better but it’s all down to the risk assessment.