Early in my sobriety I tried to make amends but it was an ugly failure... perhaps like the groaning and blaming your ex-BF is doing. You might be right to see how it goes when he leaves treatment before you jump back into a relationship. Going to treatment is getting a separation from our drug of choice - for me that was alcohol, but alcohol was a gateway drug that allowed me to do any drug in front of me. I went to treatment, intensive outpatient for a couple of months drinking regularly and still got a pass, even having them say I "might not be an alcoholic" and "alcoholism in remission". I was one one those people who can do really well with institutions. I knew how to follow the rules and protect my booze. I never stopped drinking and drank another 10 years.
The real test is how we act in the world. I have heard the phrase, "If you want to know how I am doing with AA, ask my family!" I can hold my own at a one hour meeting a few times a week and still be a terror in my home. I know because even years later I struggle a great deal with my old habit of respect via fear and yelling. My husband is as patient as a saint and remains so... but I was pretty darn bad when drinking, so any change is good... that does not make it right.
I worked through the Steps with a sponsor in AA... NOT the Steps the counselors talked about... NOT my "life History" told to the group and NOT my "interferences". They did not teach me how to LIVE life, they taught me how to cope with it (sad). They thought they were teaching humility by making people eat humble pie, but I had to DO humble acts to learn that humility was
desired. They wanted to teach me about my inner child and maybe find pity for her... and they taught ideas of co-dependence (both theories I find to be crap for me... I was cruel, no excuses). BUT I DID NOT KNOW ANY of the TRUTH about myself until I went through the book with an woman AA who went through the Steps the same way herself. I found out where I blamed people and why - I found out what instinctual fears drove me to extremism. I told them to another person
who could continue to hold me accountable to the truth about myself. I worked through what & why I needed to make amends for
without pity for my inner child or blaming my parents. AND I continue to go to several meetings a week lest I forget what drove me to the desperation of seeking this way of life, but also to hear new experiences and solutions and share my own experiences and solutions.
So you need not rush headlong into any decision about if you go back into this relationship. Some sponsors suggest the alkie wait a year before getting into one. That will be up to his sponsor & him. YOU can go to Alanon and work the Steps yourself if you like - or just find out that you are not alone in your fears... Alanon is a good place to be... there will be much love and insight there.
Peace to you cvallejo and God's speed (timing/Kairos) in All Things.

Cling to the thought that, in God's hands, the dark past is the greatest possession you have - the key to life and happiness for others. With it you can avert death and misery for them. page 124 BB