I think in the beginning she gave too much, and you took too much. you didn't appreciate what she did, so now she's doing this because she knows she deserves much better than you.
Of course, the realization comes when another guy treats her better than you.
This is a 5 year relationship, so try to make her remember what are the sweet things you have done for her.
Also, remind her of the time you spent together.
5 years of memories, I'm sure both of you have had your 'good' times, when she felt completely at ease with you.

Try to convince her that there will be much more to come in the future.

Make her stay. persuade her. woo her back, but not too desperately, because it may make you seem totally worthless.
let her know you know what she's worth, at the same time, emphasize your own good qualities too.
like what made her love you in the first place?

This post has been edited by h-yee: Apr 26 2012, 12:37 AM