I still don't get why he had to lie that he was her husband, he could've taken care of her as her brother. Anyway…
My best guesses are maybe he thought she would recall her memories back if he hold her that he is her brother (a very small probability) or he had to explain her a lot about past (childhood, family, etc).
Yeon Jin killed, Sa-ra saw but maybe because of drugs she wasn't sane and she forgot what happened, but she remembered Yeon Jin's shoes and drew it once she got home (it was showed in one of the episodes).
Great plot, loved acting of child characters. But romance between the leads after the grow up is extremely cringe. Disappointed with Kijoo and Kiyong's acting. The story that should make me cry, instead made me throw up.
Don't trust anyone.