Forget Me Not

Forget Me Not.
Five inseparable friends became four when one left without telling the others, leaving them to endure the suffering of not being able to forget.

What happens when she comes back after two years?
What happens when she probes back into their hearts once again, when they had started to forget little by little and had began to move on with their lives?

"Forget me not".
What happens when the one who had stated this in the first place, is the one to forget?