A lot of good points and interesting comments.
@Psychonaut, congrats. You did the RIGHT thing.
@Profanity, how can you always be so wrong?
That was rehtorical, please DON'T answer that.
Jealousy is an emotion just about everyone will feel at one time or another, and it's rooted by an insecurity...
If you can't deal with other guys looking over your girlfriend, or if a girl is bothered by their man liking another woman, then you're gonna have some tough times, because, there will always be an attraction for someone "else" during times of the relationship. There will always be moments where something could possibly happen. To overlook this or be angry or jealous about it is just self-destructive.
If you can't trust your bf/gf in the same room alone with someone attractive to them and of the opposite sex, then you shouldn't be in a committed relationship with them PERIOD.
NOTHING about jealousy is a good thing. It's a pain that one person feels... a fucked up combination of worry, angst, envy, impatience, unhappiness, paranoia, depression and others, and with some people blinding rage, anger and a host of other very negative feelings.
I almost forgot to mention how it affects the other person in a relationship. It's very stressful and heartbreaking. You always think about what you're going to do and how it will affect your jealous partner. You're always walking on eggshells and eventually start figuring out what makes your partner jealous, so you start lying about those things. It's a very vicious cycle, being on either end of a Jealous relationship. If the person doesn't truly love you, then you crush them. If they don't, they often do things that will make you jealous on purpose. It's one of the worst human emotions/feelings. It does nothing positive.
The best one can do is to try to occupy their time doing something else... distract themselves, reassure themselves that their thoughts are betraying them. There are legitimate reasons to feel somewhat jealous, but when it is uncontrolled it destroys relationships and people's lives.
I'm a very jealous person by nature, and at times have felt it so bad in my chest and body that it was a physically dehibilitating.
I've worked on it for a long time, and it caused a number of relationships to dissappear. Not just between partners, but friends too.
If I knew what I know now, I would have sought counseling. Not that I was destructive or hurtful, just cause I didn't need to figure out how to deal with it alone trial and error style.