Having a family member get sober is an adjustment for everyone. While we are drinking or using other drugs, our behavior and effect on other family members is considerably different than when we get sober. It is sometimes a shock to newly-sober people to discover that when they get back home things are not always sweetness and light.
We have written elsewhere about how unreasonable it is for alcoholics and other addicts to expect to be trusted, simply because they have been clean and sober for a few weeks or months. Children may feel that a parent was not there for them when they needed support. They may remember bouts of anger, even abuse of the other parent or themselves. They probably have their own anger related to missed occasions, sports events, a normal family life, and general absence of a parent whom they love and look to for nurturing.
The same is true of a spouse. In addition to all of the above, he or she may resent having had to single-handedly deal with responsibilities that should have been shared. These things may apply to older children, as well. It may even be that these members will resent the attempts of a formerly-ineffective parent to step up and fill the roles that they have gotten used to.
Some or all of these issues will exist in every family where a parent or sibling has been actively addicted. For that reason, it is critical that families undergo joint therapy, where issues may be aired and adjustments made in the presence of skilled professionals. Individual therapy may be necessary for some or all members as well. Without such help, the likelihood of further family problems is high.