I kinda think your expectations were a little unreasonable, here. If I am reading this right, you got some unexpected free time, and made plans in your head before you had consulted him. He had no reason to know of your plans, and made plans of his own--a commitment to his mom to help her with her company. I think it's a little unreasonable for you to expect him to BREAK a commitment he had already made, to spend time with you when he had no reason to know you would even have this time available. KWIM?
I don't know that it's "co-dependency" so much as just having an unrealistic expectation. Actually, I think the fact that he is keeping his commitment to his mom is a sign that he has made progress in his sobriety.
If I were you, I'd find some other nice things to do during your unstructured time off, spend a little time with him when you can, and work on accepting that he has a life of his own, too.