It has been said that love is not jealous. However, I say that true love is tinged with a bit of jealousy.
Is jealousy in a relationship ever healthy? Why, of course, but the amount of jealousy is what determines that healthiness. For instance, jealousy may prevent a partner from engaging emotionally or physically with other people. If that partner respects his or her partner's jealousy, then that jealousy has created boundaries in their relationships which, in turn, helped to foster respect. However, when most people think about jealousy in a relationship, they think that the jealous partners are insecure. They say, "If they actually did trust and respect one another, they wouldn't be so jealous." But again, this is not always true.
Trust and respect are quite different from jealousy. Trust and respect may create jealousy and jealousy may create trust and respect, but those terms don't actually influence each other. For example, I may be prone to jealousy so my significant other and I decide to create boundaries about what is acceptable and what is not. This actually fosters trust. It does not, in any way, degrade trust. Creating boundaries that determine what is acceptable or not is not saying, "I don't trust you, so we have to make these boundaries." It is saying, "I know my jealousy can hurt our relationship, and I can't help it, so to cope, we should make these boundaries for our relationship to work better." See the difference? The former phrase seeks to hurt, while the latter seeks to make amends.
Now it may be argued that the other person is losing out on something if he or she (silently) disagrees with those boundaries. What is important to any relationship is the word "sacrifice." It is a scary word to people, because one may think, "Why should I have to sacrifice something I like or something that is part of me just so I can be with this person?" A healthy relationship is one in which both people are willing to make sacrifices, whether those are material or immaterial. Some people may say that sacrifice is negative; but, in the same way that a tinge of jealousy helps bond a stronger relationship, sacrifice helps to level the playing field that jealousy is put on.
Thus, a touch of jealousy never hurt anybody. As long as it does not actually interfere with the relationship as a whole, then a little bit of jealousy can be quite healthy. It tightens bonds and it encourages mutual understanding.