(uggh, just lost my post -- oh well, here goes another shot)
Sticking just with the OP right here (although I'd like to see responses to Toonia's stuff!), I think a little bit of jealousy shows some sort of connection, and indifference is not necessarily good. If someone matters to you, their absence will feel like a loss to some degree. And jealousy seems to me to be tied to a sense of loss or, maybe more realistically, a fear of future loss.
I miss my kids when I am not with them because I love them, and I can be jealous if they spend all their time with their friends. And when I'm in a committed relationship, I miss my SO when they're not present... and if they consistently choose something other than me as the object of their affections, I'm going to feel jealousy on some level ... even if I can rationalize it and understand that what they are doing at the time is necessary. I firmly believe everyone should have the choice to come and go as they please in a relationship, you can't force someone to be with you or do what you want; but at the same time, I am not obligated to give more of my heart to someone than what part of their heart they give to me. So while you cannot shackle someone to your side, you can offer stipulations of what you're willing to invest and what you expect in return, and negotiate the expectations of the relationship.
Like Marm says, it's not necessarily the feeling but the behavior that is right or wrong. You can either respond to jealousy to control someone else or you can choose to free them and free yourself. I also think being apart is not a bad thing, because it gives both partners things to bring back to the table. I might have missed my kids when they went to school all day or went away for a week to camp or to visit friends, but it was enriching to the relationship when they brought back new ideas and experiences to share.
After ending a relationship recently, I was sort of surprised to experience jealousy when my ex told me about things he was doing with mutual friends of ours who happen to live closer to him than to me. Yet, at the same time, I was happy he was finding ways to fill his time and other relationships to be involved in, instead of floundering and feeling alone. I saw my feelings as more of a positive, since it meant I did actually care about him, missed him when he was gone, and valued what we had together even if we'd ended it. (Did I tell him about how I felt? No. I figured it was just something I needed to deal with right now.)