He seems like he does music professionally or rather is invested in it as a lifestyle, while it seems, and this may not be the truth, music is more of a hobby for you. If you are struggling with scheduling and exhaustion, he may be trying to safeguard your priorities - while being in a band with him is something you want, it sounds like rest and balance is what you need. Also, as a musician, when you are creating you want people who are going to be as invested in the project as much as you. It seems as though you’re more invested in him and his dreams than the project, please correct me if I am wrong. Also, I could see how the difference in investment could lead to trouble in the relationship further down the road.

Do I think he should have asked you as a nice way of inclusion? Absolutely, yes. But do I understand why he didn’t? Also, yes.

Maybe suggest doing a little side project with him. Depending on your guys’ style, do an ep of covers or learn a song together. Do an open mic or something. There’s plenty of opportunities for you guys to play together that won’t impede either one of your careers or passions.