They married in 1653, when Johannes was only 20. Catharina's mother objected to the match, and it appears that the couple eloped.
Courtship in 17th century Holland was a bit different from that in other western countries. If a family approved of the couple, they were allowed a "window courtship" — the young man could slip in a window at night, and leave the next morning. Such nightly visiting was called kweesten, from the word "quest." When the young woman became pregnant, a wedding followed.
Apparently Catharina was the one to slip out the window, moving in with her lover at his family's inn, and then marrying him.
Eventually Catharina's mother came to accept the couple, for they eventually moved into her large house in Delft, where they lived for the rest of their lives. Vermeer painted in the front room on the second floor (producing only 34 paintings over the course of his life).
The novel and film Girl with a Pearl Earring portray Catharina as a jealous, selfish and superficial. It should be noted that there is no evidence of this! Not a shred. Novelists and movie-makers need to stir the pot to get a good story, so this is most likely fiction.
So why do I consider Catharina Bolnes extraordinary? Simply because she gave birth to fifteen children, eleven of them surviving. [Note: some say she gave birth to 14, 10 surviving, but I believe this historian's account.]
The extraordinary size of their family was unusual: in the Netherlands, most couples only had two or three children. Clearly, this was a romantic couple, and clearly, too, they wanted children (for there were — and have always been — means of birth control*).
Although it's not known for sure, it's likely that Catharina sat as a model for her husband. (At the very least, this would have saved money; the family was financially strapped.)
Here are three that some say might be of her:
"Woman holding a balance" (Note: the woman in this painting looks pregnant.)
"Woman in blue reading a letter" (Note: this woman also looks pregnant.)
"Woman reading a letter by an open window" (Note: I think it's possible that the woman shown here might be in the early months of pregnancy.)
* A rhyme of the time: "If the apothecary would not provide certain herbs, a lot of children would be born."
For more, explore the wonderful posts and links on Johannes Vermeer and 17th century daily life by art historian Kees Kaldenbach.
I've recently posted to my research blog on the subject of pregnancy in the 17th century Europe:
Why the keen interest? For one thing, the characters of my novels are often pregnant. For another, my daughter is about to have a baby!