Astrologically speaking, if synastry reading
reveal neptune affliction - usually there will be deceptions in the
relationship. Depending on the signs and planets affected - this
could meant different degree in deceptions, secrets, untold events,
etc.
P.S: No need to find out in discreet. Ask or catch him red-handed
by accidents. No point playing a defensive game with him - if he
fools around, trust me - you will definitely know it, sooner or
later. No deception in relationship can be kept forever.
Cheers