Yes, it's tempting. When feeling betrayed, upset, angry and distraught, some divorcing (and divorced) parents can't resist the temptation to use the child who lives with them as their shoulder to cry on and their confidante. These parents burden their children with tales of their ex's excesses, sins and "issues." They want their kids to be on their side and to be as angry with their other parent as they are.
Children shouldn't ever be asked to side with one parent over another. Even when parents haven't been the best, children tend to love them and want to stay connected. Their conclusions about their other parent need to be their own, not the route to their wronged parent's love. (If the other parent is truly abusive and dangerous, the kids' feelings absolutely should be validated but their supportive parent's focus should be on protecting them, not on creating allies.)
Parents who are divorcing will keep their arguments between the adults. Most important, they know that children shouldn't be asked to shoulder problems that their parents can't seem to handle on their own. They do not ask their children to understand marital infidelity, sexual dysfunction, betrayals or disappointed love. That is the role of good friends, supportive adults in the extended family, therapists and clergy. Only other adults can provide adult support and advice. Kids need to be shielded from behaviors and emotions they are too young to understand, not used as live-in shrinks or best friends. They should never be asked to be the caretakers of the people who are supposed to be taking care of them.