Was Wormtongue's betrayal due to his his desire for Éowyn or due to the Voice of Saruman?

Question

Wormtongue was a traitor, and yet in the Lord of the Rings it is suggested that this was not always so. Furthermore, it is known that he desires Éowyn. When Gandalf says,

"How long is it since Saruman bought you? What was the promised price? When all the men were dead, you were to pick your share of the treasure and take the woman you desire? Too long have you watched her under your eyelids and haunted her steps."

Eomer reacts angrily and makes it clear that he already knew of Wormtongue's desire for his sister. Is it mentioned in any of Tolkien's notes what the reasons were for his becoming a spy and a traitor? Was it because of Éowyn, or was it the power of Saruman's voice to take control of his mind, or was he simply a man of traitorous intentions from the beginning?

Answer 1

It is most likely that he was someone who was not particularly skilled at handling the opposite sex and was not blessed with an impressive physique or other attractive qualities.

I would guess:

He fell in love with Eowyn but knew she was out of his league and was resigned to just pining for her.

Saruman sensed this and began to use his voice to twist the situation to his advantage. Probably assuring Grima that once he was powerful and helped Saruman she would notice him etc.

Answer 2

Maybe he's just a horrible treacherous person, and will do anything to get some money/power/women. If the situation had been different, he would have done something else that is just as bad.

Answer 3

Grima's betrayal is very similar to Maeglin's (of the First Age). Both of them lusted women they knew they could not get.

In the case of Maeglin, he desired his cousin Idril. Unfortunately for him, "the Eldar wedded not with kin so near". Knowing this, he became angry and jealous, these feelings grew upon the arrival of Tuor, who then wedded Idril. Finally, when Morgoth captured him, Maeglin turned to evil and betrayed Gondolin.

Thus all seemed well with the fortunes of Maeglin, who had risen to be mighty among the princes of the Noldor, and greatest save one in the most renowned of their realms. Yet he did not reveal his heart: and though not all things went as he would he endured it in silence, hiding his mind so that few could read it, unless it were Idril Celebrindal. For from his first days in Gondolin he had borne a grief, ever worsening, that robbed him of all joy: he loved the beauty of Idril and desired her, without hope. The Eldar wedded not with kin so near, nor ever before had any desired to do so. And however that might be, Idril loved Maeglin not at all; and knowing his thought of her she loved him the less. For it seemed to her a thing strange and crooked in him, as indeed the Eldar ever since have deemed it: an evil fruit of the Kinslaying, whereby the shadow of the curse of Mandos fell upon the last hope of the Noldor. But as the years passed still Maeglin watched Idril, and waited, and his love turned to darkness in his heart. And he sought the more to have his will in other matters, shirking no toil or burden, if he might thereby have power.

Thus it was in Gondolin; and amid all the bliss of that realm, while its glory lasted, a dark seed of evil was sown

Now what about Grima? Well, we have no idea when Grima started lusting for Eowyn, but it was presumably when he first saw her (in womanhood). Knowing he would never get her, he resorted to "haunting her steps" and "watching her under his eyelids" -- basically stalking her. Finally, Saruman, needing a spy in Rohan, convinced Grima to betray Rohan.

In both cases the delusion of getting the woman they desired by betraying their kindred was implanted into them, by Morgoth and Saruman. It was because of this that they turned to evil.