Leo decided to take Erren to his parents' house where there would definitely be someone to look after Erren when he wasn't home. Seeing her gestational age and growing belly, Leo couldn't just stand by. However, he was afraid that something would happen to Erren.
At first, Erren didn't want to, he didn't want to be apart from Leo, but of course Leo insisted that he had to be with someone, at least with his Aunt, who did live at his parents' house.
And in the end Erren agreed even though he felt heavy-hearted. He felt uncomfortable because he didn't know Leo's family very well. Especially with his condition of being pregnant first, and suddenly Leo said that he would marry a girl who was pregnant with his child.
Erren's feelings at that time were raging when he heard that it turned out that some of Leo's family did not like Erren. They still think that Erren is a girl who seduced Leo to get pregnant and all because she needed Leo's money and wealth.