Tips for relieving anxiety when my son starts overnights with his dad

My son will be just shy of 15 months, his dad wasn’t involved in the pregnancy at all and has zero experience with infants so when we went through court they didn’t order them but suggested we work toward it a few months after his increase in time that happened when our son turned 1. His dad has a history of alcoholism which seems to have improved, he also has a fiancé who does the majority of my sons care which I’m so thankful for, but I still worry. I have an older son and the experiences I have with my younger sons dad are that he slept on the floor with my son once, but also wanted me to tie the door shut and let him cry himself (in his new bed and new space) to sleep at 22mos. And that man I knew was too drunk/passed out to function the majority of the time. Sooo I worry. Though many of the issues seem to have improved I’m just worried sick about my son being ok, being treated with love and understanding, and also really have never spent a night away from him. Any helpful advice?