Was Ravana revenging the dishonor of Shurapanakha by kidnapping Sita?
No; he was driven by lust for Sita, not love for Shurapankha.
After Shurapanakha’s nose was cut and her brothers Khara and Dushaan were killed singlehandedly by Rama, Shurapanakha went temporarily mad with fury and frustration, and wandered about crazily in the forest before thinking of going to Ravana. Meanwhile, the only survivor from the army at Janasthana, a warrior named Akampana, fled to Lanka and informed Ravana about the destruction of his army. The incensed Ravana wanted to immediately take revenge, but Akampana, being a shrewd warrior and having seen Rama’s prowess, cautioned his king that Rama was way too powerful and had best be left alone. Though Ravana didn’t like this advise, he abided by it remembering that the boon he had from Brahma didn’t guarantee him protection from humans.
Later, when Shurapankha came to him and insulted him publicly for doing nothing to protect his own sister’s honor, Ravana became outraged at the insult, resolving to take revenge. But when he heard that Rama and Lakshmana were the cause, his inclination to take revenge subsided visibly. Seeing this, Shurpanakha, knowing her brother’s insatiable lecherousness, decided to trigger his lust by describing Sita’s matchless beauty. Then she further spun a story saying that she had approached the humans just to get Sita for Ravana, while actually she had had no thought of Ravana at all at that time – she was simply lusting for Rama and had even tried to murder Sita when she had perceived that Sita was the obstacle to her getting Rama. But Ravana his intelligence destroyed by his inflamed lust bought into Shurapankha’s story and set off to abduct Sita.
According to some retellings of the Ramayana, Shurapanakha had her own axe to grind. When Shurapankha’s husband, a formidable demon, had started becoming too powerful for Ravana’s comfort, that demon-king had conspired to have his brother-in-law killed. Shurpankha had come to know of Ravana’s role in making her a widow and wanted to take revenge. But given Ravana’s power and boons, she couldn’t do so herself. So when she saw Rama’s unparalleled prowess, she discerned that he was strong enough to kill Ravana and decided to do whatever it took to make him angry with Ravana. Accordingly, she instigated Ravana’s lust so that he would go after Sita, thereby making him provoke Rama’s anger and court destruction at his hands. Therefore, whether the core issue was of Shurapankha’s honor is itself questionable.
Further, if the issue had been of honor, what honor was there for him to abduct Sita behind Rama-Lakshmana’s back? If he had been really in the mood of a brother wanting to revenge his sister’s dishonor, he should have challenged Rama or Lakshmana to a duel and defeated his opponent in a fair fight. To avenge the perceived dishonoring of one woman by victimizing another woman is cowardly and barbaric.