That is a good question.  The answer is that his temptation was absolutely real.  Just because we do not give in to a temptation does not mean that we were not tempted.  In fact, as a Christian, I only give in somewhat rarely to the temptations that I feel, but I do feel them often.   The Bible describes Jesus as human in every way, yet he did not sin.  The passage is Hebrews 4:15.  That is why Jesus makes such a great high priest.  He can empathize with us, because, as the writer of Hebrews tells us, he was tempted in every way, just as we are.  He was tempted with anger, with tiredness, to be jealous, to be impatient, and these are ones that we can directly observe in the gospels.  I am sure he was also tempted to lust, and tempted to lie as well as many other sins that we do not see directly in the gospels.

It is his human qualities that endears so many of us to Jesus.  The most obvious example of Jesus being tempted is found in Matthew 26:36-45.  We also find this in the parallel passages in Luke 22:47-53.  Jesus was sorely tempted to not go through with the suffering of the cross.  His emotions were so intense that capillaries in his forehead burst.  He begged God to let him not go to the cross, yet, though sorely tempted, he said to his Father, “Not my will your will be done.”  This was no mere theatre.  Jesus was sorely tempted, yet he did not sin.  He is the only human to have reached adulthood without sinning.

You say that Jesus cannot sin.  I think what you meant is that Jesus could not (ie past tense) sin.  Could Jesus have sinned?  He was God-in-the-flesh, after all.  So, surely he could not have sinned.  This seems reasonable.  Yet, to say this ignores the humanity of Jesus.  Yes, he could have sinned if he had so chosen to.  And that is the point, and what makes him the Great High Priest (Hebrews 2 and 4).  I hope this helps.

John Oakes