Truth and Consequences by Constance M. Burge
When Phoebe agrees to an innocent drink with a friendly stranger she finds that good intentions are quickly misconstrued when Cole arrives early to surprise her and is stunned to find her sharing a drink with another man. Their escalating argument about trust and betrayal leads them to the underworld where they find themselves trapped at the centre of a lovelorn Demon's plot to destroy the Power of Three. If Cole and Phoebe can't reconcile their suspicions and insecurites there's more than their own relationship at risk!