Look, this is the nature of domestic abuse, you have spent such a long time trying not to irritate him that now he is in trouble you are thinking it is your fault.
As someone said above, he must have done something very serious for the police to take it seriously, it takes a LOT, absolutely a lot for them to go to this level, they may know more than you do, they may know that he is ready to potentially hurt you and therefore might be keeping him in for your own safety and your child.
You may be thinking it wasn’t that bad because you may have got used to this or even worse kind of behaviour, and that is some kind of thinking you will need to snap out of it, it may take years but keep in mind that the important thing is not anymore to keep him happy for your own safety, he us out of the house. The important thing now is to keep him at a long distance to ensure you and your kid can have a life without fear.
It will be difficult, but hang in there, keep your distance, don’t back track, you will get there in the end and will manage to provide a safe life for your child to flourish without toxicity or abuse at home.
Hang in there, you are strong enough, remember this is all about keeping you and your child safe.