How can it be so hard to let go?

I'm heartless and just don't care, or maybe I've never been in true love. Either way I have a hard time understanding why it's so hard for women to just let go. Maybe I shouldn't put it down as just women. I'm sure there are some men out there who are also finding it hard to get over a relationship.

I have a family member who's going through a recent break-up. Now I say recent to be respectful but if we're going to be accurate it's been coming on for some time. But sometimes we just go through the motions. For comfort, because we're scared, whatever your reasoning may be.

But when it's over, why can't we just accept the fact and move on with our lives? Why do we torture ourselves? Now I understand there will be a period of grief, because in a sense you are in fact, losing a loved one. But a part of grief is moving on. How can you move on when you throw yourself into situations where you will inevitably come in contact with the person you're trying to forget?

Perfect example. This person is out shopping for the day, like mall shopping not going for groceries. This is the point, she goes to Joe's while she's out. For those not familiar with it, this is a chain of sporting good type stores around here. Now, she;

*Doesn't camp
*Doesn't play sports of any kind
*Doesn't fish
*Definitely doesn't hunt

What is her purpose for going there? To buy ex-boyfriend some new work shirts because you see he likes to wear the nice Carhartt shirts and she was in the area and she knows his truck has things wrong with it so to make a trip all the way over there would be really hard for him. Oh and before she moved out she had noticed that his shirts were getting a bit raggedy so why not go get him some new ones while she was there. No wait it's better than that, she has to SPECIAL ORDER them because the ones they have in his size are of a color that he would never wear. So let's get 2 of each of the 4 colors he does like...and I'll just have to go ahead and buy them now, well shoot I'll have to because the only way they let you special order them is to pay in advance.

So the next day as she talks to ex-boyfriend on the phone, she casually mentions to him "Well I was in Joe's getting something for me..." (LIES!!!) "And I knew your shirts...blah blah blah" I'll spare you from all of that again. Then when he doesn't jump for joy and sing her praises with his thank you's she gets all upset and pouts for the rest of the day. As if the magical relationship fairy was going to come and sprinkle love dust on this dead relationship in the form of 8 new Carhartt T-shirts from G.I. Joe's.

1. It's just an excuse to talk to him on the phone. Which then leads to the OMG I miss him so much depression.
Why do this to yourself??

2. It's also a "see look what I did for you don't you miss me doing things for you?" thing.
Again. Why do you do this to yourself??

I just don't understand. Maybe I am, like I said, heartless and uncaring because I feel like when it's over, it's over. Get over it and move on.