The marriage seems clearly to be over. And if it wasn't on his first day back from Argentina, it's hard to conceive how it isn't now.
That isn't to understate all the damage and hurt he's caused to his family, his children and his supporters; let alone the breach of faith with his constituents, not over the affair but over the dereliction of duty. But notwithstanding his claims that he wants to stay in office and repair his marriage, Sanford's every action suggests overwhelmingly that he is desperate not only to get kicked out of office but to get kicked out of his marriage as well.
Everything he's said seems geared to reach back out to his mistress in Argentina (to perhaps re-cement the possibility of continuing the relationship?) and force a final breach with his wife. It is almost as if his upbringing, culture, religion and simply familial obligation require one thing but he's doing everything he can to make those requirements beyond his capacity to fulfill. Put simply, it's like he wants his wife to cut the cord for him.
Of course, when you're a middle-aged man facing the collapse of your life's work and abandoning hope of being with the woman you call your 'soul mate' rational decision making or a clearly considered plan may be too much to expect. But it does seem like there are two guys here. One saying he wants to serve out his responsibility to his state and reconcile with his wife and another using the press to broadcast a free form love poem to the girlfriend in Argentina.