Carpenter's Gothic Ending

Towards the end, it's clear that Liz is having an affair with McCandles but Liz's death isn't very clear. It isn't described how she's dead in the house but I assume that the reason why is because McCandles realized that Liz has everything that she has and has always rely'd to much on Paul in order to start a new life with him. Though, it isn't explained how it happened but we learn at the end of the story that Paul pretty much used Liz for money and his own benefit and the relationship sadly never had any meaning at all.