There was a healthy handful of divorced passengers on board.
In addition to JJ Astor and Lady DG, the list includes:
Helen Churchill Candee
Harriette Crosby
Charlotte Cardeza
Eleanor Genevieve Cassebeer (from first husband, Mr. Long, if I remember correctly from a thread on her several years ago)
Erik Lindeberg-Lind
Olive Earnshaw was in the process of a divorce and Dorothy Gibson had separated from her husband and resumed her maiden name, but I don't think actual divorce proceedings were underway (this is partly according to Randy Bryan Bigham's excellent work, and so perhaps he can confirm).
I'm sure there were others in second and third class who I can't think of off-hand. Of course, many passengers went on to be divorcees, though most in later decades. Among those who divorced within the era of the sinking (say before 1920) are the Carters and the Bishops.
Those who were eventually divorced from the people they were married to at the time of the sinking, whether a few years later or many years later, include Zette Baxter Douglas, Samuel and Nella Goldenberg and Albert and Sylvia Caldwell. I had thought Emma Schabert was divorced from her husband before marrying Baron von Faber du Faur (as opposed to being widowed), but a glance at her ET bio does not confirm this.
I have read that Clinch Smith was returning from an unsuccessful attempt to convince his wife to live with him again, but I can't recall which book I read it in and don't know if it's true. However, Edith Bowerman Barber, Margaret Brown, Ben Guggenheim and Emma Bucknell (though her husband had died by 1912) are all examples of how couples at the time were much more likely than they are today to remain married and lead separate lives long after finding living together intolerable.