Hi
My LO is almost 5 and has supervised access with his father due to domestic abuse and mental health issues.
Dad collects him from my house and a member of my family facilitates their time together.
This morning my son said maybe his daddy would come into the house, to which I had to say that wouldn't be happening. This led to difficult questions such as "why can't he come in?"
He also mentioned that his dad doesn't know we have cats, and I explained he does as he lived here for 6 months before we split up (while I was pregnant) and met the cats then. This led to more questions, such as "why doesn't he live here any more?" so I explained as best as I could that sometimes people don't get along and decide not to live together any more. His reply was that we need to fix that 
I'm finding it really hard to think of the best way to handle these things in a way that is age appropriate. I don't want to put his dad down at all, but I can't tell the truth, which is that he was abusive, so I had to ask him to move out and then had to call the police because he was abusive when I used to let him back in for contact, so now I can't trust him and don't want him back in my house again.
I'm really conscious of trying to keep things positive so that my son isn't negatively affected and of course not involve him in parental difficulties, but these questions are really difficult, my answers feel inadequate and I'm sure there will be more to come as he gets older.
Any advice on the best way to handle this is welcome.
Thank you.