Spider's Trap (My Thoughts)

 A spider lures it prey, attracting it, and later dispose of it.

This is similar to what I have seem with one of my friends,
She is what you can call a girl who like attention, she likes it when people complement on what she wears and that she is pretty. She goes to parties sometimes not for the food, but for people to tell her what she is wearing look pretty on her.
Another friend of mines fell for her, and asked her out. Now.. by this time, she had dated 5 other guys which she dumped or was dumped. These dates lasted for about 1 week to about 1 month the most. This relationship, was where the guy liked the girl, but it was not the same for the girl. So after a month or twp, the girl decided that she just wanted them to remain friends. The guy was depressed for about 1 week till he recovered and was able to act normal again.
Now I believe it is happening again, another one of my friends probably fell for her. He probably asked her out and she said yes. This time, whether or not she is truly likes the guy or not, it only depends on how long they last. What I don't get is how come the girl can easily date someone and dump them so easily later. Does she really want attention so bad that she had to date someone, or can she just be satisfied with the attention she is getting from her friends now.
If they are dating, I am a bit worried for my friend, because I don't want him to be another "prey" in the spider's trap and left sad in the end.
People might say that its non of my business what is happening, but they are both my friends and I don't like it when one of my friends emotionally hurt another.