You know that because Blade is afflicted with mara, Kafka often uses Spirit Whisper on him, which causes pieces of Blade's memory to simply disappear.

You knew about this.

But why did it suddenly become so painful when Blade woke up after another attack of mara and looked at you and narrowed his eyes?

"Who are you?" Blade’s words rang in your ears.

You knew this would happen one day. You knew, but... the fact that Blade forgot you was unexpectedly painful.