Hugs
What a painful situation. I am glad you understand that this is not about you. He MUST put his recovery first and it is actually a good sign that he is taking it seriously enough to make it the priority.
I expect that he is also doing this because he does care for you, and realizes he is not able to be in a relationship. He's not ready, and he may not want you to wait around etc.
I hope you can understand what I am about to say and not take it as if I am accusing you of being his problem.
In our lives and relationships we establish certain patterns, habits and dynamics. And we get into comfortable routines. When we get into recovery we begin to see how we must change many things in our lives other than just not drinking/using. Because if all of our other patterns and routines are in place, it makes it much easier for us to slip back into drinking/using again. Like ruts in a road.
That doesn't mean everything in our lives was wrong or that all the people in our lives were bad, but sometimes we must set those things aside for awhile, or even permanently in order to establish healthy patterns.
The intent of recovery it to learn to live as a fully integrated member of society, but sometimes at the start we do have to focus on recovery and protect ourselves from some challenges we are not ready to face.
What feels like rejection to you, might be him taking some honest responsibility for himself for the first time in a long time.
I know that doesn't make the hurt and loss any less. I have experienced the same situation. But reminding ourselves that it is not about us can help us progress in a healthier manner.