あの家を買っておかなかった事を後悔している。

that (someone or something distant from both speaker and listener, or situation unfamiliar to both speaker and listener)

house; residence; dwelling; family; household; lineage; family name

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 buy; to purchase; to value; to have a high opinion; to stir; to provoke

to put; to place; to leave (behind); to establish (an organization, a facility, a position, etc.); to set up; to appoint (someone to a certain position); to hire; to employ; to place (one's trust, one's faith, etc); to bear (in mind etc); to put down a tool (e.g. a pen) hence stopping what one is doing with that tool; to take in (boarders, etc.); to provide lodging in one's house; to separate spatially or temporally; to do something in advance; to leave something in a certain state; to keep something in a certain state

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