Asked whether this film would be the last of the Doinel cycle, Truffaut answered (with Claude Jade standing next to him) quote, "with this film, he [Doinel] reached adulthood and there's no reason to go on." Of course, this is completely wrong. He did make another one, "Love on the Run," proving how difficult it is to predict the future course of a creative process. As for the other comment, it was probably meant tongue in cheek: Doinel does indeed "reach adulthood" agewise here but that's not the same thing at all as maturity, which is the point of the film, made with Truffaut's flawless Mozartean touch and clever cinematic style.
Having seen all five, what struck me is that, except for "400 Blows," the stories are as much about Doinel as about the women in his life, played by Marie-France Pisier, Claude Jade, and Dorothee, showing what a charmed life the fellow led and how lucky he was to have crossed paths with so many beautiful women, an autobiographical point because it's well known that Doinel=Truffaut. We come away from this film realizing that encounters with Beauty are not appreciated for what they really are, a favor from the gods. No sooner that his wife, the sweet, delightful, and adorable Christine (Jade), has a baby that Doinel decides to cheat on her with a Japanese woman! Truffaut doesn't properly resolve this matter until later, in "Love on the Run."
A word about the title. "Domicile Conjugal" is a rather literal title in French that does not mean "Bed & Board" or anywhere near that. And yet "Bed & Board" is entirely appropriate given how casually Doinel treats house and home with the lovely Christine and their baby. Bravo to whoever thought of the English title.