Character Analysis
Martine's boyfriend really is defined by the way he introduces himself: he gives all of his many names upon first meeting someone. Martine says that this reflects his "old-fashioned" nature, or his unwillingness to give up the customs of everyday life in Haiti. He's someone who can't let go of his old life in Haiti, as Martine snarkily observes:
"Marc is one of those men who will never recover from not eating his manman's cooking [...] If he could get her out of her grave to make him dinner, he would do it." (7.53)
Because of this, Marc's an interesting choice for Martine. She can't spend any time in Haiti without her nightmares getting completely out of hand (even worse than they are in New York, apparently), so it would seem that she wants to leave her old life behind. Her choice of Marc shows that she can't let go of her old life—or that she wants to take the best of her past and try to move forward.
After Martine's death, Marc gets on Sophie's bad side because he doesn't wake up in time to save her mother. But he's also the person who makes all the arrangements to fulfill Martine's wishes to be buried in Haiti. Even Sophie in her grief admires his way of breaking the news to her ("She is rather in the morgue"), even if part of her blames him for Martine's final crisis.
Marc Chevalier's Timeline