probably not. :( I think that when a married man cheats, he's looking to recapture his curteous, Don Juan-ish behavior. He will act gallant, and he will fulfill your wishes, all the while seeking conflict at home, to justify long absences. Every man who cheats speaks of a devilish wife, who doesn't understand him, but in truth, that connection was simply weakened by the fact that he no longer desires her exclusively, and by lies.
Now every situation is subtly different of course, but if he were to leave his wife, and marry you, how do you know that in time he would not come to lie to you too? If there are, or if there would be children involved, they will suffer, pointlessly, because of the conflict that surrounds them.
In your current position, you are enjoying only half-a-man, the charming side, and not his full personality. He's still trying to conquer you... Try to ask yourself if you really are content living half a life. You deserve a man who loves you completely, a man who'll be with you in his good times and his bad times, and not just as an escape from a situation that's become trite.