I was with my husband for 17 years, married for 9, and lived together since we were 17 years old. I'm 34 now. We should have separated a few years ago but sort of simply held on because of how long we'd been together.
While my husband didn't ignore me, he did eventually ignore what I needed in a relationship so he could live precisely how he wanted to, even if it was a strain on me. But the culprit is that we got together so young and figured out what we needed while we were in the relationship, so looking back, it was a gamble that we'd grow together and not apart.

Something you mentioned that resonated with me is that you provided significant financial boosts to your life together in the form of buying your first home. You also supported him in his career and managed what sounds like some toxic stuff from his family.

I share your experiences with this. I purchased our first, second, and third home; his toxic family became more and more of a burden (his alcoholic mother lived with us while she was on house arrest because of her multiple DUIs). He struggled with jobs until finally, five years ago, he gave up on his career altogether to pursue his art full-time.

Maybe this will help, and maybe it's not applicable to you, but something I've discovered in my separation is this: some men derive a lot of self-worth from being the "provider" or the "rock" even if they don't realize it or even want to be the provider/rock. I bought our homes because I wanted us to have a nice home, not to make him feel like less of a man, but it did make him feel like less of a man even if he didn't know it then. I didn't help him with his family drama just to have him feel embarrassed by them, but he did. I didn't take on all of the financial responsibility, so he felt like a deadbeat, but he did.

In the end, I did all of these things because I cared about his happiness, but all it did was make him feel worthless, so he looked for self-worth from other people outside of the relationship.

Your ex may have been happy with the dynamic the two of you had, but after a few years, his own view of himself may have become damaged. So he escaped into drinking with friends at all hours, most likely because it was fun and an ego boost.

He couldn't tell you why he was unhappy because I bet it was all of the things you did to support him. He twisted all of your support around and turned into a judgment of himself. He should have been the one to pay for the house, his family shouldn't be so messed up, and he shouldn't struggle with work. Healthy people accept and appreciate love and support from their partners; they don't let it become a wedge in the relationship.

Again, I can't stress enough that I'm not saying this is what happened at all. This is what happened to me. Now I know, moving forward, I will only get into a relationship with someone who has a strong sense of who they are, what they want, and are already working positively toward those things. I also know that my ex and I didn't work because we just didn't want things with the same intensity, so me just being me ended up making him feel insecure and unaccomplished.

It's a shame you haven't gotten much of a reason from him for what happened. Which my ex couldn't do at first either. That's why I thought I'd share.