I felt bad about picking on him.
Watashi wa kare o ijimeta koto o kōkaishita.
I; me; private affairs; personal matter; secrecy; selfishness
topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis
he; him; his; boyfriend
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 tease; to torment; to persecute; to chastise
thing; matter; incident; occurrence; event; something serious; trouble; crisis; circumstances; situation; state of affairs; work; business; affair; after an inflectable word, creates a noun phrase indicating something the speaker does not feel close to; nominalizing suffix; pretending to ...; playing make-believe ...; alias; aka; nickname; alternative name; also known as
regret; repentance; remorse