彼は教師になろうと心に決めている。

he; him; his; boyfriend

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

teacher (classroom)

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 become; to get; to grow; to be; to reach; to attain; to result in; to prove to be; to consist of; to be composed of; to succeed; to be complete; to change into; to be exchanged for; to play a role; to be promoted; to do ...

if; when; and; with; particle used for quoting (with speech, thoughts, etc.); quoting particle; promoted pawn; indicates question (sentence end)

mind; heart; spirit; the meaning of a phrase (riddle, etc.)

to decide; to choose; to determine; to make up one's mind; to resolve; to set one's heart on; to settle; to arrange; to set; to appoint; to fix; to clinch (a victory); to decide (the outcome of a match); to persist in doing; to go through with; to always do; to have made a habit of; to take for granted; to assume; to dress up; to dress to kill; to dress to the nines; to carry out successfully (a move in sports, a pose in dance, etc.); to succeed in doing; to immobilize with a double-arm lock (in sumo, judo, etc.); to eat or drink something; to take illegal drugs