Get real, so many asumptions in that it reads like a piece of propaganda
Women are geneticaly programmed to "get attention" it doesn't mean she's unfaithfull or being "slutty" by dressing up on a night out.
And i'm amazed that you have the power to get inside her mind and know that she's out to consciously get attention from lads on this night out. You best be carefull or the goverment will kidnap you, lock you up in some secret bunker and do exsperiments on you to learn your super power
If he has no past reason not to trust her, then let her have a good night out with her friends irespective of wether they are dressed in armour or Burlesque gear.
Its not about her it's about the OPs own insecurities, he needs to learn not to let them rule his life and by connection his Girlfriends.
If he finds out she was unfaithfull then get rid, If she feels he's emotionaly restricting her then she'll eventualy get rid.
Thats life, live with it..