I don,t have enough faith to be an agnostic, the evidence is too much man. I was once a skeptic, but as i started reading and researching i couldn't find a reason for it to be false.
The best is that she knows the thruth, if you fuck the other chiks, don't be a cockblocker and get jealous or mad when she does it. If she does everything right, invests in you, is submissive, is feminine, values you, makes your dick hard whenever you like, respects you etc. Then there is no reason to cheat on her.