How exactly did Yaakov 'steal the heart' of Lavan?
Targum Onkelos and Targum Yonasan: By simply not informing him of his plan to run away. Ohr ha'Chayim - had he done so, Lavan would have guarded against this.
Seforno: By pretending not to know that Lavan had accepted his sons' Lashon ha'Ra, and not to notice that his friendly disposition towards him had changed.
Tosfos ha'Shalem (1, citing R. Efrayim): Lavan planned to steal all of Yaakov's property. Since Yaakov took it, it is as if he stole Lavan's heart.
Malbim: He made it appear that he is not fleeing, so no one told Lavan.
How could Yaakov leave his host of twenty years without saying 'goodbye'?
Seforno: He did not do this out of ill-manners, but because he was afraid that Lavan, with the help of the people of the town, would steal from him. 1
Ha'amek Davar (to 31:21): Hashem did not promise to protect him from Lavan, and it was not easy to remain on the road a long time without Lavan finding out. He hoped that Lavan would not find out for a while, but Hashem arranged otherwise. In any case, He saved him. 2
Harchev Davar (to 31:21): This is a Siman for his children. When they trust in Hashem to be with them on their path, Hashem annuls their counsel in order to pain them, refine them or for another reason; but in any case, He saves them in a way they did not expect. Yaakov chose this method, for it is not against human choice.
Why does our Pasuk refer to Lavan as "Lavan ha'Arami"?
Ramban (to 31:24): To teach us that, despite the fact that Lavan was a sorcerer who divines with Terafim, Yaakov succeeded in 'stealing his heart.' 1
Seforno: To explain why Yaakov stole Lavan's heart (Refer to 31:20:1:2). Because, had Lavan realized that Yaakov was aware of his feelings, he would have placed obstacles in his path to prevent him from leaving.
Ha'amek Davar: Even though Lavan was a master trickster, Yaakov succeeded in 'stealing his heart.'
How could Yaakov have informed Lavan that he was fleeing?
Targum Onkelos and Targum Yonasan: "Bore'ach" means (not that he was 'fleeing' but) that he was 'leaving in haste.' 1
Oznayim la'Torah: The Pasuk means that Yaakov did not inform Lavan (not that that he was fleeing, but) because he was fleeing.'