彼の言葉を信じてはいけない。

he; him; his; boyfriend

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

language; dialect; word; words; phrase; term; expression; remark; speech; (manner of) speaking

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 believe; to believe in; to place trust in; to confide in; to have faith in

if ... then; when; and; why don't you...?; the more (one does something); because; since