If she cheats on you it is probably because of your lack of confidence/insecurity, or your lack of trust.
Just saying, a man is more than a dick...
Nice, if she cheats on you it's your fault. This is a painfully ignorant load since you don't know any more than he's told you.
Bottom line, if you know you've fucked something up to cause her to grow distant and cheat (yes, cheat) on you over naughty messenger then fix it. If you haven't then you need to ditch her fast cause she WILL hurt you. Only you know which it is. Don't be afraid to make the hard choice but make sure it's the one that makes you keep your self esteem intact. Don't go out on a limb for someone who's going to saw it off.