My boyfriend and I split after the birth of our second son. Our first son is 1. He moved in with the mother of his first child. She has a 2 bedroom apartment with 3 other kids living there. My boyfriend constantly smokes weed and does not have a job. IVe also heard his girlfriend smokes meth and abuses pills. He also had his license taken for delinquent child support with his other kid. He went to jail in 2012 for a domestic violence Assault on the girlfriend he lives with now. He's never successfully completed probation or his domestic violence classes. Idk if it'd matter but he also has a domestic violence with this girl on his juvenile record. He just got charged with domestic violence harassment for threatening to kill me and take our sons. I know that his new girlfriend also had domestic violence cases with other guys. On the basis that this place is not a safe environment for kids would supervised visitation be considered?

With the pending domestic violence charges I would say yes. What you have "heard" is not evidence and won't be considered by the court. Concentrate on his public record.