acolytes,
Well, he disobeyed because God told him NOT to do it, that is the disobedience.
The "sin" came from his use of his free will to do what he knew was wrong and against God's commandment.
You bring up his love for Eve, but there is no indication that Adam ate the apple t o please Eve or because he loved her so and wanted to be with her.
6 When the woman saw that the fruit of the tree was good for food and pleasing to the eye, and also desirable for gaining wisdom, she took some and ate it. She also gave some to her husband, who was with her, and he ate it.
and after God confronts him:
11 And he said, “Who told you that you were naked? Have you eaten from the tree that I commanded you not to eat from?”
12 The man said, “The woman you put here with me—she gave me some fruit from the tree, and I ate it.”
No where is their indication of "love" being the reason for disobdience, they BOTH knew it was wrong and they BOTh knew the consequences and they BOTH did it KNOWING it was wrong, hence: Sin.