Divorce typically marks the beginning of a child's family transformation, not the end of it. After all, when parents divorce they don't merely go their separate ways and commit to a life of romantic celibacy. Both partners typically set out to find another mate, entering new dating relationships on their path towards eventual remarriage. Among those who divorce, roughly three-quarters will remarry (Krantz, 2011), which means that 3 in 4 kids will have to endure this family restructuring at least twice more during their childhood, and possibly more if you factor in live-in partners or additional divorces and remarriages. These new relationships and family arrangements bring with them added challenges for parents and children alike.
Whether rightly or wrongly, children tend to interpret your pursuit of new interests and a different life as a rejection of them. (Wallerstein et al., 2000) So as parents try to move on with their lives, children often feel as though their own desires are being left behind. As the quote above suggests, they were perfectly happy with the old family and their role in it, and so your pursuit of an all new family arrangement with all new people is seldom met with enthusiasm. Children are often suspicious of what these new arrangements will mean for them, and rightly so. Much like their fear of abandonment, a distrust of your new pursuits is not entirely irrational. Just as many kids do have a parent drop out of their life after divorce, many children suffer adverse fates as their parents move on to new romances and stepfamily situations. Even in the best of circumstances, building a new relationship with someone involves time and devotion, and this must come from somewhere. Often kids instinctually sense that these pursuits may come at the expense of time spent with them.
These situations also add more turmoil and instability to a child's life. Each transition means additional stress, changes, and adjustment, and each one takes its toll. Studies suggest that it typically takes around 2 years for children to adjust to a new stepfamily situation. (Hetherington, 2003) More concerning still is research that shows children in stepfamily situations typically fare no better, or even slightly worse, than those kids who remain in single parent households. (Amato, 1994; Sobolewski, 2004) This is notable, since remarriage brings substantial improvements to important areas like family income and human resources, which are two of the most influential correlates to child wellbeing. So the fact that child welfare measures don't track upwards alongside remarriage suggests that most children are ending up in stepfamily situations that are less than ideal, and that the additional conflict, stress or disruption in these situations is eroding any benefit that should otherwise come with improved financial and family resources.
The stress created from these changes is often overlooked by adults, but consider for a moment how they can add up. Many parents divorce when a child is young, and some may endure yet a second failed marriage before remarrying for a third time (around 60% of all second marriages end in divorce). So if you take each of these family adjustments (let's say mom remarries once and dad twice) and multiply them by the 2 years of adjustment each will require, and it's easy to see why many children of divorce feel like they never recover the stable foundation they enjoyed before the divorce. If parents divorce when a child is 5, and it takes a couple of years for them to recover from this, and just when things were settling down for them dad remarried, and so they had to adjust again, and then at age 9 their mom remarried, and they had to adjust again, and then perhaps mom divorces once more and remarries again sometime in their teen years, causing yet another adjustment each time, and you quickly reach a point where you've essentially spent your entire childhood in perpetual transition. Given such circumstances, it's easy to see why many people consider the divorce as the day their childhood ended; the moment when a stable family environment gave way to perpetual instability and family dynamics that were always in flux.
These mish-mashed family dynamics also create more opportunities for things to go horribly wrong. Sadly, the old fables about evil stepmothers and parents abandoning their kids when a new wife comes along are only partially based in myth. Such fictional stories are built upon a very real phenomenon that is as old as the ages: biological ties can and sometimes do matter. Some people have a strong nurturing instinct and will readily adopt and nurture any child that comes their way. But others aren't so accommodating, and humans also have within their nature the same instinct towards preferential treatment that causes lions to kill the cubs that aren't their own whenever they take over a pride. This reality is reflected in everything from how resources are allocated between kids to the rates of child abuse in step-parenting environments. (Children living with unrelated adults are as much as 50 times more likely to die from abuse as those living with blood relatives; Begley, 2009) Not everyone is so thrilled about having to devote time and resources towards the progeny of a stranger, or worse yet, a loathed "witch" who you despise for being the thorn in the side of your new romance. Throw into the mixture a dabbling of defiant behavior by child towards unwanted stepparent, and it makes for a situation that can quickly degrade into chaos.
So when parents remarry, it often does create loyalty issues. Many new partners DO secretly (or perhaps not so secretly) loathe the offspring that their new mate is encumbered with. Conflicts do commonly spring up between stepparents and stepchildren. There are stepparents who make it their mission to degrade and devilify a stepchild and who try to disrupt the parent-child relationship, and some parents do end up choosing a new mate over their own children. Horrifically, many children of divorce do become "leftovers" as the parents move on to assemble a new life with new families that leave them stranded at the periphery edges. Around half of stepparents will evolve into nurturing caregivers for their step kids. But the other half remain more or less disinvolved, if not outright resentful towards the offspring of their new spouse. (Wallerstein et al., 2000)
It is sad realities such as this that lead many parents to wonder whether they should even try to remarry. This is a personal decision, and we would never steer you away from it, other than to say you shouldn't rush into remarriage just for the sake of it. Follow your heart and go wherever the romance takes you. If you find someone you think is a permanent companion, go for it.
The good news is that mixed in with these horror stories are a number of happy endings. There are people out there who will come in and love stepchildren every bit as much as their own, thus enriching a child's life rather than diminishing it. There are stepfamilies that get along without creating conflict between the new partner and the former spouse. There are parents who handle these transitions in a way that reduces the strain on kids. You just have to be sure to approach these shifts with prudent caution, and with empathy towards your current children and what these changes can represent for them. You want their story to end with love and belonging, not the toxic, displaced stepfamily environment indicative of Cinderella.