The Darker Side of Terror (1979)

"What happens when you create the world's first perfect human ... and he turns out to be your wife's perfect lover?"

A psychological thriller about a research biologist who, angered when an associate is given a position over him based on stolen research findings, agrees to assist his former professor in a cloning experiment in which a duplicate of himself is created -- and which then, with a mind and will of its own, falls in love with the biologist's wife.