彼は喜びに我を忘れた。

he; him; his; boyfriend

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

joy; delight; rapture; pleasure; gratification; rejoicing; congratulations; felicitations

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

obstinacy; atman; the self; the ego

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

to forget; to leave carelessly; to be forgetful of; to forget about; to forget (an article)