This is an early 20th century postcard by Bamforth, a British company with a long history in the postcard & film business.
This card is poking fun at several things, but in the end it displays a succinct understanding of the human condition. (I mostly wrote the previous sentence to see if anyone was paying attention).
Most people who do not live together do not really know each other. If the only place you see someone is at work, or behind a counter, you don't really know them.
If you don't live with someone, you don't experience the undesirable sights, smells, stains and/or bodily fluids that can no longer be hidden. Humans are a biological species and as such are a messy sort, but that can be hidden or diminished UNTIL you live with someone.
After marriage, a husband (and wife) with almost certainly be different than he (or she) appeared before.
Anyway, that's what I think. Bamforth is a great company that produced thousands of postcards - many slightly (some more than slightly) risque. And a lot that are just a little odd.