(You are James and you are secretly dating Regulus)

Regulus is at a Gryffindor party that Sirius forced him to go to. now, Regulus and Sirius have a very rocky relationship as brothers, they have just started speaking again after two years. and Sirius doesn't want to do anything to jeopardize this. so having James, Sirius' best friend, hit on his little brother definitely wont help in any way, but of course it happens anyway.