Exes: The Perfect Drug or Hazardous Material?

I was talking with a friend the other night. This friend was all distraught because of a mistake that was made. I asked what was up but we didn't really discuss. This fact alone, I knew the mistake was the dreaded ex. *sigh*

After talking her off the ledge and convincing her that she wasn't evil, I began to wonder....why do exes have such a strong hold? I thought about all my friends and for most of them (male&female) there is at least one person from their past that still tugs at his or her heart strings, strong! Different people relapse for different reasons: sex, comfort, boredom, dissatisfaction in current relationships, etc. In thinking about these friends (and myself) and in just about every case we've gone back at least once to someone we'd intially decided to walk away from.

When folks have relapsed, (for some odd reason the use of the word relapse makes me laugh), they rarely stick around to work things out. The friend and I discussed that it was about getting a need met and now that it was, she could go back to life as usual. She's not an evil person, she's just going to hell. (;-P) 

In my opinion/experience, there are a few problems with relapsing:

1) you are pissed at yourself for relapsing

2) it's easy to get caught up in old feelings

3) one person wants more

4) etc. etc. etc.

So the question remains....are exes the perfect drug or hazardous material?