So now we come to understand Lois' state of mind when she wrote her story.

She was lied to, but what's worse is how everyone continued to lie to her, even after she had discovered the truth. If only they could have had an honest conversation, where she felt included in their lives rather than excluded, things might have turned out differently.
not all poisons are fast-acting. Some are slow and insidious, building up in the bloodstream until the luckless person collapses with a system already too corroded to be healed.
Such a great metaphor for the entire story!

She is poison to him. His own personal Kryptonite.
Yeah...she should feel like this, heartbreaking as it is.
He cannot be Superman while she drags him down.
He cannot be Clark while she lifts him up before the whole world.

From now on, Lois Lane is just as dead as what-might-have-been, and there is no going back.

Such an important decision she's making here, walking away from Clark, doing the right thing for his sake, giving up whatever might have been between them, because it's the right thing to do. Sad, but right.