In a comment below, Jonathan Prejean (formerly of Crimson Catholic) refers to the Third Council of Constantinople, which condemned Monotheletism, the heresy that Jesus possessed only one will.
Monotheletism is one of those heresies -- or if you prefer, ditheletism is one of those doctrines -- that's hard to get overly worked up about. Granted that we're perfectly willing to assent to the belief that Christ possessed both a human and the Divine will, the question remains, what are we supposed to do with this belief?
a heresy ... intent on removing the perfection of the becoming man of the same one lord Jesus Christ our God, through a certain guileful device, leading from there to the blasphemous conclusion that his rationally animate flesh is without a will and a principle of action.
As with so many heresies, Monotheletism strikes at the Incarnation, without which we're all pretty much just Shriners. The Council defines the orthodox dogma in these words:
Believing our lord Jesus Christ, even after his incarnation, to be one of the holy Trinity and our true God, we say that he has two natures shining forth in his one subsistence in which he demonstrated the miracles and the sufferings throughout his entire providential dwelling here, not in appearance but in truth, the difference of the natures being made known in the same one subsistence in that each nature wills and performs the things that are proper to it in a communion with the other; then in accord with this reasoning we hold that two natural wills and principles of action meet in correspondence for the salvation of the human race.
Moreover, as they explain just before this definition:
And the two natural wills not in opposition, as the impious heretics said, far from it, but his human will following, and not resisting or struggling, rather in fact subject to his divine and all powerful will. For the will of the flesh had to be moved, and yet to be subjected to the divine will, according to the most wise Athanasius.
So Jesus' human will, even in Gethsemane, did not resist or struggle against His Divine will.
And yet: He ... began to feel sorrow and distress. Then he said to them, "My soul is sorrowful even to death... My Father, if it is possible, let this cup pass from me...." He was in such agony and he prayed so fervently that his sweat became like drops of blood falling on the ground.
We know, then, that having a human will perfectly subject to God's will doesn't mean never feeling distress. It doesn't even mean always desiring, of one's own volition, what God desires, though of course it does mean always choosing what He desires. We are not called to agree with God, but to obey Him. But obedience is the road to perfection, and the more we obey God, the more our human wills become, not merely subject to His, but genuinely like His. I speculate.