Strangers with Candy (SPOILER)

“The Comfort of Strangers” has many of the common “Travel Fictions” built into it. Like many couples, Mary and Colin have gone to Venice (if I can call it that) in order to reignite a dying flame. They have the expectation that travel in foreign places will rekindle their love. What is uncommon about the plot of the book, is what begins to happen to them in this foreign place. The beginning of the story takes place as one would expect. The two have not found anything new in their lives, despite the strange new surroundings, and instead have established a routine as they might have back in America. It is not the new place which incites their newfound love, but instead, it is a new person. Somebody who scares them both, and with whom they both seek to avoid encounters. It is not clear at first what makes them uneasy around Robert but one can assume that his mannerisms impede their “personal bubbles”. Especially once it becomes apparent that his definition of love is dying for or killing someone else. He shares too much information, too soon.
Only after this encounter do Mary and Colin fall back in love. What is it about what happened that makes them grow closer together? Was it their mutual fear of these strange people that caused them to look for more in each other? Or did the love of Caroline and Robert simply bring out the love which Mary and Colin had for each other? I know that Caroline and Robert certainly would throw me for a loop. But the end of the book left me with a lot of questions. I guess in the end Colin dies for Mary, which is the ultimate proof that their love had been rekindled. Yet why did Robert and Caroline do so? Was it something that turned them on? Sure, they were both exited by pain, but isn’t it the other’s pain, or someone with whom the subject is involved what causes Sadomasochism? Not simply a random stranger. In the end I suppose that the only explanation has something to do with the way that both couples dealt with the encounter. They somehow were both exited by the meeting. Caroline claims that she and Robert were more passionate after seeing Colin, and the reader is shown quite enough evidence to see the same thing happen with Mary and Colin (although these two do not seem to know the causes). Does the foreign aspect of the book have to do with the new passion? Is it simply the chance encounter of someone else, a couple who could have been anywhere, not just Venice? I must admit, I was severely confused.