jail is not rehab
In rehab, if you truly want it, you learn the tools to stay clean and to
recover, not just quit.
I think he is feeding you a line of excuses for not getting in rehab so he can
move back in with you when he gets out.
Has he said that yet?
If he hasn't, expect him to.
Needless to say, this would be a serious mistake.
I'm sorry he's spent more time in jail than you both expected, but
that is no reason for him not to get the help he really needs afterwords.
He stole from you once--don't set yourself and your child up to be stolen from
and manipulated again.
If he is serious about recovery, he will show you.
Meanwhile, keep your distance financially (no letting him live there)
and wait to see his actions, don't just listen to his words.