Johann Sebastian Bach and Maria Barbara Bach had a happy marriage and in that time seven children were born. One of the duties at the court of sovereign Leopold was, to accompany him on journeys, which absolutely could last for a longer time. What might be interesting to know for that period of Bach's life is, that Bach could even picture himself living in Köthen forever, to make music and to compose. But it came different.
Coming back from such a trip with his sovereign, who was his friend too, he learned, when opening the front door of his home, that his wife had died during his absence. They still don't know today, what caused her death. A second bad blow for Johann Sebastian Bach was, that they already had to bury his wife without his presence.
Of course there's the big question, whether Bach finally married a second time, because he had to deal with his many children, his household plus his job. That would be a clear answer to a strange question. On the other hand this was a very common reason to marry soon again back then. Single parents households were a rather unusual family construction around 1700. However, opinions of biographers are very controversial. If I would have to decide, I would tend to believe that Bach married a second time, because he fell in love with Anna Magdalena. Bach's wedding with her didn't take place earlier but eighteen months after the death of his first wife. At that time his children have surely got accustomed to a household without a mom. Plus, Bach within a time of eighteen months surely had accomplished to organize his household in a way, that worked better from week to week, as in a large family more siblings with growing age get used to the fact, there is no mother around. It's hard, but it's the way it works.
Anna Magdalena was an artist too, she was an educated singer and she earned good money at the court of Koethen too. So she didn't marry as well for the reason, somebody had to care about her. So the question is left open, why actually Johann Sebastian Bach married a second time.
99 Music Calendars, Composers Calendars and Bach Calendars