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If it's really short — no more than a few paragraphs — set it off with italics. It should quickly become apparent from context who the first-person-italics character is. If it's pages and pages, ...
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#4: Attribution notice removed
Source: https://writers.stackexchange.com/a/28580 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#3: Attribution notice added
Source: https://writers.stackexchange.com/a/28580 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
If it's _really_ short — no more than a few paragraphs — set it off with italics. It should quickly become apparent from context who the first-person-italics character is. If it's pages and pages, make the husband's parts interstitial bits between chapters of Sam's story, and label them as **Sam** and **Dean** or whatever. Labeling the chapter by the POV character when you have multiple POVs in a novel is very common and easy to follow. Don't write four pages of italics. It's visually exhausting.