What is the ironic device in this quote John Proctor says, I have gone tiptoe in this house all seven month since she is gone?
John says this when Elizabeth tells him to go to Salem to talk to Abby and that is when John explodes and gets angry.
This line occurs in a particularly uncomfortable scene in The Crucible. John, we've discovered, has had an affair with the "dissembling" Abigail. We've also discovered he has no intention of being with her, since she gave him that opportunity again in Act I and he denies her--something he did on his own, not because Elizabeth was mad or was somehow aware of their encounter.
Here, Elizabeth is telling John about the trial (they'd both been out of touch with the proceedings in town), and John is dumbfounded, telling her he knows the girls to be frauds. This opens up the entire episode between John and Abigail at Betty's bedside. John apparently told Elizabeth everything about the encounter--except for the fact that he and Abigail were alone when it happened.
Elizabeth simply makes a few statements, but they're enough to work on the already guilt-ridden John. The lines which come before the line you mention is:
You forget nothin' and forgive nothin' Learn charity, woman.
I have gone tiptoe in this house all seven months since she is gone. I haven't moved from here to there without I think to please you, and still an everlasting funeral marches round your heart.
And there's more.
The irony of these lines is that Elizabeth has, indeed, forgiven her husband. The problem is, hehas not forgiven himself. This, of course, is the crux of his dilemma at the end of the play when he must lie and live or tell the truth and die.