They had a one-night stand, so depending on the circumstances... tipsy or drunk... it’s possible to have a vague memory! But, he actually has a clear memory of her; she just keeps denying their tryst!
Yes, they did have one stand, but it dosent mean they didnt know each other before that. Like he has the photo of her back and from the way he talked about her they seem to be acquainted. She knew his resident well, like when she knew the short cut. So she must has worked there or been there a lot. This meant that he knew her and it's not just stranger hit it up with each other. He also said that he only love her, at least the old her. So this mean he knew her freaking face. The only logical explanation for me right now is some type of amnesia or plot whole. It's make no sense to me for someone to forgot the face of someone they loved without a medical reason.
Why can't he remember her face? Was it an amnesia? Am I the only one who think it's weird that he didnt remember his "old friend" face.