It's definitely not genetic and you do not have to be in a weak relationship to be jealous at all. Jealousy is a natural thing and it does not always become a problem in all relationships. I like my bf to act a little jealous. To me it shows he cares about me. What would I think if some guy tried to talk to me and my boyfriend just stood there and didn't mind? I'd think he didn't like me as much as he let on.

My response is based on personal experience and observation, so I stand to be corrected.
Jealousy is a natural and sometimes very strong emotion that we experience from a very young age. I’m sure you are familiar with ‘sibling rivalry’. Children aren’t born with a healthy self image and are very insecure. Parents then build their self confidence by paying them a lot of compliments, and give them a feeling of security by hugging and cuddling. Yet, when a new baby arrives the older sibling will become jealous. This is because the child does not have a strong enough self esteem to deal with the little newcomer.

Jealousy in relationships sometimes works on the same basis. If a person does not have a strong self esteem, every person of the same sex is seen as a threat, regardless of their appearance, age or social status.

Another reason people get jealous is if they know that they themselves cannot be trusted. These people will constantly accuse their partners of cheating. (this is personal experience speaking)

People with emotional baggage from a previous relationship (in the form of an unfaithful partner) will also project these feelings of insecurity on their new partners.

Just as there are different reasons for people to feel jealous, people on the receiving end of jealousy react differently to the situation. Willa for instance feels secure in the fact that her boyfriend is a little jealous. She interprets it as him loving her. (And she’s most probably right)
I just get annoyed out of my skull. Lol. I’m not the type of person that will EVER cheat and my boyfriend should know that by now. Regardless if I spent the entire evening talking to an elderly gentleman 70 years my senior, who has probably been impotent the past 20 years, a gay youngster, or Brad Pitt.

I know this is an old post, but felt I had to reply.

Jealousy is natural and in most cases adaptive. Both men and women get jealous, because they have found a partner they want to stick with and don't want anybody trying to steal them away. It all comes down to basic human nature, but it can also be learned. My ex, for instance, was so jealous and I couldn't talk to a guy without being accused of flirting with them. If I said I was going out with a male friend on my own, he'd get all huffy and say 'make sure nothing happens'. I lived with this for 4 and ahalf years and I'm sorry to say that eventually I gave up being faithful because I thought if I was being accused of it I might as well go ahead. I'm not proud of that and I accept responsibility for it but if he had trusted me then I wouldn't have done it. Anyway he told me his family were all jealous, and he picked it up from them, but he also had very low self-esteem. He even said to me when we broke up that he didn't want to be alone and he was scared he would never find anyone else. I think that's why he stayed with me for so long.
My current boyfriend doesn't get jealous of my friends, or if I talk to other lads, or if I say I'm going out with some guy friends, and I love him for it. I would never cheat on him as long as he trusts me.

If a man can get ‘stolen away’, I’ll help him pack. If he’s not trustworthy – let him be on his merry way.

Mandy, don’t say things like:’ I would never cheat on him as long as he trusts me.’ There really is no reason for cheating. If a guy is constantly accusing you of cheating: just leave him. Don’t let him make you ruin your own reputation, because that is ultimately what will happen: you’ll get a reputation as a ‘player’ (as we call them here.) You’re a lovely, attractive girl, and I’m glad you found a good man now. Just do the right thing, okay Hon?

Yeah, I've learned my lesson now. I definitely should have left him before anything happened, but we'd been together a long time and I'd grown used to that way of life, I was too scared to be alone. I'm not excusing myself for what I did. Also, he wasn't 100% innocent either. Anyway it's all in the past now, I'm moving on and forgetting about it. I learned the hard way about the consequences and I'm never doing it again.

Good on you, Babes!