The ending of The Ambassadors: Why Strether runs away

As I said upon finishing Henry James's Portrait of a Lady: How could you?! I'm saying it again on finishing The Ambassadors - a daunting, challenging, often exasperating, sometimes incomprehensible novel, whose plot, when you come right down to it, is pretty simple: 50ish widower sent by his similarly 50ish fiance, the wealthy Mrs. Newsome of Connecticut, to Paris to "save" her son, Chad, and bring him home to run the family business (pointedly, the characters never dare to mention exactly what object of manufacture has made the Newsome fortune) finds himself free at last in Paris and more or less in love with a beguiling woman with a dark past, Miss Gostrey. Ultimately - end of novel - Chad decides to stay in Paris with the older married woman whom he loves, Mme de Vionnet, and the protagonist, Lambert Strether (great name), get this, decides to go back to Connecticut. Novel ends with a series of heartfelt dialogue meetings: amazingly, Strether is deeply distressed and shocked, shocked!, to learn that Chad's relation with Mme de Vionnet is anything but chaste and pure. They actually take off for a weekend and share a room and presumably have sex! I know mores and times were different 120 years ago - but not all that different. The world must be peopled. Finally, Strether has a long meet with Miss Gostrey in which he tells her how deeply he feels about her - but he's going back to Connecticut. What a coward, what a bastard! He actually ends by thanking her for loving him - but has no problem leaving her in the dust as he returns to the staid, comfortable life of Connecticut, a life he will hate. He is a heartless and selfish man, there is no other way to look at it - except that also, you have to suspect, he is running away from the sexuality and sensuality of Paris. All's well when he can engage in these lengthy conversations with Miss Gostrey, but when confronted with the image of sex in a relationship, that is, when he learns to his shock and shame aout Chad and Mme de V., he runs away - a sad and sorry little man. The busybody Mrs. Newsome deserves him, and he her.