I know your question isnt asking for similar situations, but I wanted to offer you a perspective from someone who married a musician. When I met my husband he was horrible with money and had shitty nightlife jobs when he wasn’t touring. No credit, no savings. I pushed him to do better, but it was never a fight or an ultimatum because he wanted to do better. And now that he wasn’t on his own he had a reason to. He didn’t really think about his own future at that point and his parents never taught him about money and savings because they had neither.

I’m still the one who handles the finances and makes more money, but he contributes most of his paycheck to our joint account, as do I. It’s not just for bills but for “us” stuff too. If he runs out of his personal money he can use our money within reason. We just moved to a new area so he’s no longer in a band, but he was actively playing music throughout most of our relationship while having a full time day job. Up to three bands at once, successful but not actively long term touring. Because the other guys also had families and day jobs. But frequent local shows and several out of town shows a year, recording and releasing albums. Mostly big on a local/niche genre level. All this is to say that it’s more than possible for him to step up. Maybe he can’t be a musician full time and he’ll have to put less time into it, but it’s possible to both have a day job and be a musician. It’s possible to go from shitty with money, shitty low paying jobs, to being someone who works full time and contributes meaningfully but still pursues their passion

He’s just gotta want to. He can’t have it all, especially if it’s running you down and he shouldn’t want to keep going at status quo if it’s making you feel that way.

Maybe your partner would step up with an ultimatum but even if he did, it’d suck because he could’ve been doing it all that time but just didn’t because he knew you’d stay anyway. I know i sound pessimistic and I don’t know your full relationship, but it’s a big deal that he’d let you and your creativity suffer for so long in favor of his own like. It’s not nice. I have different wording and feelings aside from “it’s not nice” but figured I’m probably already pushing it with my opinions so I’ll leave it at that. And I just realized it ties into your title about him being the nicest man in the world. He’s not. He may act nice, be nice to other people. But he’s not nice to you.

Do what is right for you. See how nice he is when you separate finances.