I feel your pain. I, too, connected with an old love from younger days. I had minimal understanding of addiction - and a few months into our relationship he told me that he still did "cocaine" from time to time. Ummmmmmm... it was more like crack and occasionally IV cocaine. He got clean, I believed in him, we were true loves, we got married. He stopped working a recovery program, became verbally/emotionally abusive, would apologize and beg for another chance. Finally, after 5 years of misery with him he choked me and threw a plate at my head. GOOD BYE.
I didn't leave him sooner because of how financially entwined we were and the HEAVY duty hit I would take if I left him. He had moved into my home and then wouldn't leave. I had to move out of MY OWN home to get away from him.
Speaking with an attorney is important. And getting support to help you resist the upcoming barrage of apologies and pleas that you are going to receive sooner rather than later is important.
I hate this for your child. My boys were profoundly damaged by going through this experience (my ex was their step father). The only thing that I could have done that would have damaged them further would be to have stayed even another moment longer.
I know this feels overwhelming but you can get through it.
I really hope that your story and my story will make even one person think twice about merging finances with an addict or a newly recovering addict. I so wish that I had waited for at least 5 years before I even thought about any of that. My ex held it in the road long enough to dupe me.
Keep posting - there is a way out of this...