彼はすっかり商売に打ち込んでいる。

he; him; his; boyfriend

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

all; completely; thoroughly

trade; business; commerce; transaction; occupation

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

to drive in (e.g. nail, stake); to hammer in; to hit (a ball, etc.); to drive; to smash; to fire into (e.g. a crowd); to launch (e.g. missiles); to lob (e.g. grenades); to input (data); to enter; to devote oneself to; to go heart and soul into; to throw oneself into; to go head over heels for; to practice hitting (baseball, tennis, etc.); to hit (an opponent in kendo, boxing, etc.); to get a blow in; to invade one's opponent's territory (in the game of go); to place a stone in an opponent's formation; to pour (concrete, etc.) into a form