What would you consider 'cheating' ?

Your friend sounds like she has detached herself from any sort of serious commitment,sleeping with other people so casually not calling it cheating is just a selfish act to keep things free flowing with ease,her conscience must be hiding in a lost and found bin.Bottom line is she cares for noone but herself that's why she claims trust is just to keep you "in check" from doing what you want,trust is a responsibility but it brings about the good in people.Treat others as you would yourself,in this case she had no respect for herself and therefore no respect for others.