Kono Koi wa Jiko desu! - Fuku Shachou to Watashi no Wakeari Doukyo Seikatsu

Asuka, a secretary at a major construction company, has had a crush on Koya, the vice president, for three years. She has given up on the idea that it is a love that will never come true, and has decided to quit her job. Then one day, a car accident causes "a problem" between them...! As soon as they start living together with a deadline until the problem is solved, Koya declares his engagement in front of everyone! Asuka is perplexed by this emergency situation, but Koya's forceful but single-minded gaze moves her to fall in love with him...!

(from mangaupdates)