1)
Why did he love David so much?
1.
Divrei Yakov Bi'urei Agados (5): He sensed that the Ru'ach Hashem that was taken from him is with David. When they were together, an influence came from David, and to some degree it returned to Sha'ul.
2)
What is the meaning of "va'Yhi Lo Nosei Kelim"?
1.
Radak: David carried Sha'ul's weapons.
2.
Malbim: David was elevated to the point that he had someone to carry his weapons. 1