Melibea introduces herself on page 1 as a virtuous woman, and brushes off Calisto as a "selfish fool".  Much of the story revolves around Calisto's wooing of Melibea, using Celestina as a go-between.  I do not really understand the type of society where using a bawd is the preferred way to obtain the love of a chaste lady.  But apparently it works, when a little black magic is involved.  Hmm.  By page 116 Melibea has done a complete turnaround and begs "Destroy my honour, damage my reputation, hurt my body, break my flesh, extract my bleeding heart."  The one character in the novel who might be expected to stay innocent gives it up pretty easily.

Calisto is one of the most self-centered characters in literature.  Obviously he is willing to risk some danger for some short-term satisfaction in Melibea's garden, so to speak.  He also is unconcerned about his servants' deaths, when his most immediate concern on page 148 is how this will hurt his own reputation.  He deserves his rather pathetic death.

The death of most of the characters in a story is an easy way to end a novel or a play.  Shakespeare obviously uses the same techniques in many of his tragedies.  However in this novel, where the volume of the dialogue seems to be cranked way high, it gives a very abrupt flat ending to the story.