  NGC 1313 X-2 is one of the few known pulsating ultraluminous X-ray sources
(PULXs), and so is thought to contain a neutron star that accretes at highly
super-Eddington rates. However, the physics of this accretion remains to be
determined. Here we report the results of two simultaneous XMM-Newton and HST
observations of this PULX taken to observe two distinct X-ray behaviours as
defined from its Swift light curve. We find that the X-ray spectrum of the PULX
is best described by the hard ultraluminous (HUL) regime during the observation
taken in the lower flux, lower variability amplitude behaviour; its spectrum
changes to a broadened disc during the higher flux, higher variability
amplitude epoch. However, we see no accompanying changes in the optical/UV
fluxes, with the only difference being a reduction in flux in the near-IR as
the X-ray flux increased. We attempt to fit irradiation models to explain the
UV/optical/IR fluxes but they fail to provide meaningful constraints. Instead,
a physical model for the system leads us to conclude that the optical light is
dominated by a companion O/B star, albeit with an IR excess that may be
indicative of a jet. We discuss how these results may be consistent with the
precession of the inner regions of the accretion disc leading to changes in the
observed X-ray properties, but not the optical, and whether we should expect to
observe reprocessed emission from ULXs.
