Welcome to SR, I hope you find some peace of mind here.
Nothing you did or didn't do cause him to use or head to rehab. While he may appear to be trying he isn't making any effort to maintain his sobriety outside of rehab and sadly, isn't responding to you in any kind of positive way.
You gave it a good try, maybe take a step back and take care of "you" now. He's on his own path and not likely to change, sorry to say. Recovery looks like recovery and actions speak louder than words.
You deserve better than this. Trying to stay in touch with him just makes it worse. Try taking your own "time out" and during that time, maybe try some meetings for yourself, like Al-anon or Nar-anon or CoDA, or reconnect with some of your old friends and get together for coffee or a movie or a day in a park...something that will take you outside of this cloud and maybe even make you laugh a little.
One day it won't hurt so much because the person responsible for your happiness is you alone, not him.
I hope you find a healthy path that helps you get past this journey into addiction.