Where does “ese” come from?

Ese comes from Spanish ese, derived from Latin ipse meaning "self" or "that very one."

ese (English): dude, man

Definitions

Step	Language	Word	Meaning
1	Mexican Spanish	ese	The name of the Latin-script letter S; that;...
2	Latin	ipse	himself, herself, itself, the very, the actual;...
3	Proto-Italic	*e(s)peso	—

ese — Etymology, Origin & Word History | Etymology Explorer