Autumn's Concerto (2009)

In both dramas, they fall in love with the main character and are forced to break up. After the breakup, the main character finds out that she is pregnant. over time they will meet and everything will turn out well the family will be together.

In both series there are lovers that are separated then are reunited.
There are other similarities that are spoilers for both series.

Both have love triangle and a the male lead has lost memory.

Both have unplanned pregnancies and the couples in both dramas are constantly misunderstanding each other.

Hyun Jae is only 19-years-old, but he has a terminal illness and he does not have much time left to live. He leaves the hospital and goes back to high school. There, he falls in love with Soo Min.