Do you want someone to cheat on you?
If you do, then fuck the girl, because sure as eggs is eggs, a relationship born of infidelity will end in infidelity. If you have a partner who is prepared to cheat on her man with you, and does it well enough to stop her man from knowing, then she will do it to you at some point.
And you know what? Even if she doesn't you'll never be sure she isn't planning on it. The fear will eat you up.
My advice?
Go for it.
OK, OK, you know I mean "don't do it".