Because you're not holding his feet to the fire about getting help beyond his existing medication. You're not working to figure out what the root cause of his recent issues are.
Loving him is fine and all, but at the end of the day we're all responsible for our own bullshit, even if we have extenuating circumstance surrounding it. It's still our problem to own up to, and take care of. He's not doing that, either because he can't, or because he doesn't want to. Which is it?
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."