The Great Divorce

So, let's look at this as if all characters are alive in body, but not in mind (not their own, but other's). Lavvie and Alan's marriage never seemed to have any life, even the children required some form of a medium to communicate with their father. He doesn't seem to ever be too terribly concerned with any of the children, but he actually makes an attempt at reconciling his marriage, which is self-admitably "dead as a doorknob". Lavvie never appears to have been happy in this relationship, and Alan wonders if she has a boyfriend.
Laura has always been second best to Sam. He stills thinks fondly, and almost dreamily, about Popsicle. Sam, on the other hand, has been cheating for his entire marriage with the notion of Popsicle as his lover, thus depriving Laura of his undivided attention. He never develops a true connection with his wife, and therefore the only connection he has is to eat undigestable materials in order to prove some level of devotion. He must always compete for her attention because he has to prove that he would do the same for Laura as Paul had done for Popsicle.

Well, here are my questions: Do Sarah and Alan strike up a relationship together? How about the bougainvillea; what is its significance? I did find that according to one web page, its purpose is, "For healing the emotional legacy of one’s ancestral line, inherited through parents, grandparents, etc." (http://www.gentlebirth.org/archives/spiritl.html) Does this belief enhance the story? What is the connection between the two stories (i.e. Sam and Laura and Alan and Lavvie), beyond the cousins, Sarah and Fred?