Sookie’s physical slaps across Bill’s face in episode 9 made her opinion on his “suicidal” decision pretty clear. But Eric didn’t want to end on bad terms with his on-and-off again girlfriend. He arrived at her home to explain that she “deserves the world” … without him in it.
For Bill, his death is the only way that he can see Sookie happy. She swore off him and other vampires time and time again, yet she always gets wrapped up in the bloody drama. By Bill choosing to die, he believed he was giving her the chance to live in the sun, grow old, and start a family.