...jealousy
It is important here to distinguish several forms of jealousy:
  1. to begrudge somebody having what you do have yourself,
  2. to begrudge somebody having what you don't have yourself,
  3. and to desire something that somebody else has (as well).
Here, I'm addressing sexual jealousy of type 1 only. This is the type of jealousy pertinent to the widespread resentment against having multiple sexual partners in the same period. It may be tempting to treat sexual jealousy of type 1 as a special case of general jealousy of type 1. However, there are two important differences: to begrudge somebody having what you do have yourself is in the non-sexual area not a common emotion. Moreover, almost everybody agrees that this kind of jealousy is objectionable, and not something to which a reasonable man would yield. Therefore it appears sensible to treat sexual jealousy separately.

Rob van Glabbeek