Should I break these two up?

unless you have some dirt on the guy and proof to back it up don't go there. you will more than likely make their link stronger. also if you feel she is flirting with you no matter how respectful of him she seems to be, put yourself in his shoes. if she was with you would you want someone else plotting against you? her flirting with him? or else just man up and tell her you want more than the casual friends scene, see what happens. most girls prefer honest not sneaky. maybe sit back watch and learn she may not be all that.