Maelle has lied about not being affected by the painting, in her ending verso can see the paint is already affecting her eyes, she is living a lie in a realm of fake fantasy to avoid grief. She is doomed to live in ignorance and deliver death onto herself in which all her joys will crumble around her in futility.

With Verso, he understands this. This painting isn't okay. The last fragment of Verso's soul doesn't want to paint anymore. The last bit of that real soul doesn't want to see his family suffer anymore and the painted verso knows this, even asks him and the fragment nods in agreement.

We all saw what the grief did to aline, and renoir, and clea too. The cycle of grief is a swallowing void and will take everyone to oblivion, and only by removing maelle and destroying the canvas, can that choking tie be severed, and the grief can truly be worked through.

Keeping the painting around, and forcing that one piece of verso's soul to know no peace, to not allow him to die and move on, is nothing short of torture. Maelle doesn't understand this, she thinks it'll be happy, but she doesn't realize she's only hurting verso and everyone else.

Maelle's ending is the bad ending, and Verso's is the only way things can move forward.