He is referring to all the kissing. I know that line about "a wife's office" is suggestive, but I hoped it would be clear that that would go against Edmund's character to go that far. I don't think Mary would do that either, to be fair to her. She has far too much good sense to risk ruin in such a shaky engagement.
However, they've definitely done a lot more passionate kissing that he really considers proper, according to his notions of propriety, which I hoped would reflect the ways that Edmund's strong attraction for Mary always leads him just a little bit beyond his good judgment. He never abandons his principles completely (as it would be if he had slept with her), but he always manages to fudge a bit. And for a man like Edmund, that would make him feel all the more obligated to Mary--however, if they had slept together, he would never even consider not marrying her.
Thanks!