In October 2010, the UK Parliament brought into effect law that replaced the partial defence to murder of provocation with a new partial defence of “loss of control”, applicable to England, Wales, and Northern Ireland. Although it retained some key features of its controversial predecessor, the new partial defence was in part designed better to address the gendered contexts within which a large number of homicides are committed. In examining the impact of the reforms, we will focus on long-held concerns about the treatment of sexual infidelity as a trigger for loss of control in murder cases. The article undertakes an analysis of English case law to evaluate the way in which sexual infidelity-related evidence has influenced perceptions of a homicide defendant's culpability, for the purposes of sentencing, both before and after the implementation of reform. The analysis reveals that, in sentencing offenders post reform, the higher courts have failed to follow the spirit of the reforms respecting the substantive law by effecting a corresponding change in sentencing practice.