Why did Lavan say "va'Tignov Osi"?
Bechor Shor #1: Our city agreed that no one may leave without Os Sheli (my Siman). I would have given it to you! One who leaves without it is assumed to be a thief.
Bechor Shor #2: Lavan's money was dear to him like himself. It seemed to him as if Yakov stole Lavan himself.
Ozanayim la'Torah: Lavan belonged to the group of people who considered partying and merrymaking the main purpose of their lives. 1 Consequently, when Yakov fled, denying him the opportunity of making him an elaborate farewell party - as indeed, he himself explains here - it was as if he had stolen him.
Oznayim la'Torah: See for example, how he threw a big party the night before his daughter's wedding.
Why is b'Shirim written lacking a Yud?
Tosfos ha'Shalem (3): We read it like Sarim (I would have sent nobles to accompany you).