Now in response to what you are saying, I'm not saying that a partner should do things out of jealousy, I'm saying that you can feel that way sometimes and you have to control it but the idea of "it's wrong to be jealous" is ridiculous.
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I think it's perfectly healthy for a girl to be jealous in a relationship as long as it doesn't turn into an obsession. The problem is that today with all the stimuli and how artificial are interactions within young generations it's difficult to have a longlasting relationship wether any of the partners feel jealousy or not, it's not due to the feeling but due to the enviroment in which these relationships are taking place. Think about it, jealousy always existed yet relationships in previous generations (like yours) were healthier, so if jealousy already existed what could possibly have changed? Social media for example. I'm just saying.
I agree with you, jealousy has always existed, still is and the over-stimuli people get today is probably making things more complicated. I admit that it's a pretty normal emotion.
But I disagree that it's healthy even without being an obsession (refusing that your partner have friends of the opposite sex is already quite obsessive to me). I have two daughters and have a lot of younger friends, I'm no stranger to how things are going now between young (and less young) people. And I'm still convinced that being openly jealous and possessive does not bring the couple together, nor now nor in the past, it helps break it. If one of the partners already has a tendency to look elsewhere, being jealous will only repel him or her even more. As such, it cannot be considered healthy.
It's not "wrong" to be jealous, as I think we agreed, it's a normal emotion. But it is "bad" one as it is destructive and I think it's better to fight against it and try instead to trust your partner. If he or she's a nice person, it will strengthen your ties with her or him. If the partner takes advantage of it, then you're better off with someone else anyway.
One last thing: long lasting relationships are never an easy ride, never have been. It's been more than 30 years where I live that one third of the married couple break up within 3 years. There are always rough times. What makes these relationships last is to discuss, compromise and agree to reinvent the relationship once in a while. And allow some private space to both.
EDIT: Rereading my posts on this topic, I realize that I'm basically repeating the same things again and again, not a very constructive way of discussing, I'm afraid. I'll stop flooding this thread now. Thanks for the discussion, even if we disagree, it's always interesting to have different points of view. I'll read wour answer if you bother writing one. Cheers.