:)
Girl's company is owned by her family, sociopath worked for a competing company. He randomly broke up with her, saying there was no future in it, but never said why.
Psychopath turns out to be crazy anonymous stalker as well as girl's unknown half brother. He had threatened sociopath anonymously to stay away from the girl because sociopath had stolen some of the girl's company's tech designs and caused her father to kill himself. He was dating the girl to get the rest of the design, but nobody knows where it was. It's incest because he is a psychopath.
The design is the secret, the psychopath doesn't know where it is but he's trying to scare/love the girl into being motivated to find it. At the end the sociopath kills the psychopath and the girl kills the sociopath then takes the secret designs and improves on them to make the sociopath's company obsolete.