One...

..loving someone means having to accept all the chapters of her past. Some people are too open about their past and they let you know so that you won't be in a awkward situation when circumstances occur. Stuff like letting you know about his/her ex. Stories of events in the past and everything or something about her past.

I'm not sure if this applies to everyone but i guess some can relate that there will always be "ONE" person or event or something from her that would make you so mad or jealous about.

If that "one" is a person; maybe her ex, her bestfriend or just a regular close friend. Deep in your heart you knew and feel that there's no more special between her and that someone but the moment you knew that she and that "one" saw each other or talk to each other, you feel a li'l something.

If that "one" is an event; maybe an event where she and that other person shared or experienced together. Everytime you hear or see that event (e.g. Concert) you feel a li'l something.

Im not sure if what you feel is jealousy or just plain insecurity but nevertheless it would make you think deeper and sigh a little. Maybe this is just one of those stuff where you knew that you trust and love her but sometimes the heart have its mind of its own.. .sometimes...