Love Does Not See the Sun (1980)

Story is about a beautiful decent young girl who is struggling to help her family. She gets an offer from a rich man who is eager to have an heir to his wealth. He asks her to become a surrogate to his own son. His son has been married for few years without an heir. Regretfully, she agreed. The childless couple agreed for the husband to spend time with her until she gets pregnant. But things don't go as planned.