How long does it take for a memory to become permanent?

Hi,

Well I was reading about Amnesia and found this article: http://science.howstuffworks.com/life/amnesia-and-...

I am a bit weak about medical stuff, but if I understand it correctly, it says that long term memories are the permanent ones that, well, do not disappear permanently due to any kind of Amnesia (please correct me if I read it wrong).

So I was wondering, usually how long does it take for a memory to be called a long term memory and become permanent?

For example, say a couple loves each other for about a year, and the entire year they stay with each other, think about each other and love each other dearly. And after a year, one of them suffers amnesia. What are the chances he/she will forget her dear love?

PS: Yeah I know kind of sounds like a movie or whatever.