彼が行ってしまおうといようと私は平気だ。

I don't care whether he leaves or stays.

彼(かれ)が行(おこな)ってしまおうといようと私(わたし)は平気(へいき)だ。

Kare ga okonatteshimaou to iyou to watashi wa heiki da.

彼 (かれ)

he; him; his; boyfriend

が (が)

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

行う (おこなう)

to perform; to do; to conduct oneself; to carry out

と (と)

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

要る (いる)

to need; to want

私 (わたし、わたくし)

I; me; private affairs; personal matter; secrecy; selfishness

は (は)

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

平気 (へいき)

coolness; calmness; composure; unconcern; all right; OK; okay

だ (だ)

be; is; indicates past or completed action; indicates light imperative

Readings: ヒ、かれ、かの、か.の

Meanings: he, that, the

Readings: コウ、ギョウ、アン、い.く、ゆ.く、 -ゆ.き、 -ゆき、 -い.き、 -いき、おこな.う、おこ.なう

Meanings: going, journey, carry out, conduct, act, line, row, bank

Readings: シ、わたくし、わたし

Meanings: private, I, me

Readings: ヘイ、ビョウ、ヒョウ、たい.ら、 -だいら、ひら、ひら-

Meanings: even, flat, peace

Readings: キ、ケ、いき

Meanings: spirit, mind, air, atmosphere, mood