One day at a time... its always a good thing to remember. Since he's back in jail, you have time to think.
You can't solve problems that have not yet come up (like custody battles, etc.), but you can prepare yourself for them by focusing on strengthening yourself from within and knowing your rights.
I have found for myself that answering the question "How should you cut off ties with an addict?" becomes easier to answer when you have made the decision within yourself that that is what you really want and why you want it.
If you are there - maybe try what has worked for me - write it down, and read it every day.
If you are not there yet, maybe explore what's getting in the way of you seeking freedom.
And, if you are worried about a custody battle, maybe consider starting to document all of his behavior, seek his criminal records (much of that is public) and build the documentation that would help you if/when this arises. And, do some reading or seek the assistance of a lawyer (many counties have free lawyers you can consult if you can't afford one) to find out your rights. That could go a long way in calming your fears. (and of course, if he continues to use, it is unlikely he will have the presence of mind to bring a legal action anyway).
A psychotherapist once said to me "the way out of a bad feeling is a positive decision followed by action". Maybe think about - What positive decisions can you make for yourself and your baby to strengthen yourself and prepare for the future.
Wishing you clarity for your next steps. Keep what helps and discard the rest.