No matter what your age, when a parent remarries it can be difficult to accept and adjust. If you are still at home and now find yourself living with a stranger, obviously the adjustment is trickier still, especially if the parent they've replaced is loved and missed. But even full-grown adults with children of their own can find the experience tough.
The greatest novelists and film-makers are often said to possess "sympathetic imagination." Shakespeare, Dickens, Tolstoy and numerous others were able to sympathetically imagine what it must be like to be a teenage girl in love, an abandoned orphan, a frightened soldier, and so on. In other words, they were able to inhabit other bodies and other minds and imagine what it is like from the inside. But most of us have this capacity to some extent. Indeed, if society made more of an effort to nurture and cultivate it, the amount of cruelty and evil in the world would be greatly reduced.
So begin by placing yourself inside the mind of your mother or father. Let's say your mother has died and, within six months, your father brings home a new woman. You are still grieving for your mother and feel outraged, seeing it as nothing less than a betrayal or insult. Now try and see things from your father's perspective. It can often take time for children to acknowledge the fact that their parents are flawed and fragile human beings rather than all-powerful, all-knowing gods. Recognizing this is a sign of maturity (and it is worth adding that maturity has little to do with age: some 12-year-olds are big enough to accept this, while some 40-year-olds behave like spoilt brats). Maybe your father is lonely. Maybe he is frightened and in desperate need of affection and tenderness.
And now consider your mother or father's new partner. Obviously you may simply dislike them as an individual, regardless of their status as your new step-parent. But if they seem perfectly nice, cut them some slack. You have no idea what kind of life they have lived or how it feels to meet you. They may have spent years feeling lonely and unhappy. Perhaps meeting your mother or father is the best thing to have happened to them. Maybe their childhood was abusive and traumatic. Maybe their first marriage was a painful disaster. You just have no idea until you get to know them. Almost certainly they will be nervous and apprehensive about meeting you, and no doubt they will hope for your approval. This gives you a degree of power – and thus responsibility.
Your parents do not exist solely to raise and love you. Some children, even in middle-age, seem to regard their parent as a kind of "carebot": lifeless and motionless until they need them, rather like a hoover or toaster! But they are separate, distinct beings with needs and desires of their own. They also need love, intimacy and romance. And they are entitled to it.
Your parent does not need your permission, by the way. The chances are, however, that they would like your blessing. At the very least you ought to be tolerant and respectful. This can prove especially difficult when money is involved, though it must be said that your parent's money is their money. If they choose to spend it on a cruise for themselves and their new girlfriend, that is also up to them.
Of course, it is easy to give such advice, and it must be stressed that circumstances differ. In some cases, especially if you are still young, this new person may genuinely affect your life in a negative way. If you are a teenage girl, for example, and your mother's new boyfriend makes you feel uncomfortable (walking into the bathroom when you take a shower, staring at you as you sunbathe etc), then you do have the right to speak out. Now your life is being affected, and this is unacceptable. The same is true if your stepfather is a bully who belittles and intimidates you. It is only true to say "it's not about you" so long as this new person does you no harm.
In some cases, the opposite danger exists and people try too hard. Either the child or the new parent so wants things to work out that they rush it. This is especially common when both parties long to be part of a happy family. But you cannot force such things; it takes time for intimacy to develop and for an inner bond to form. And your opinion of this new person may well change – not always for the better. They are not a replacement for your mother or father, remember. They have not come into your life with that in mind; they are in your life because they are in a relationship with your mother or father. The relationship between stepchild and step-parent is its own unique thing, which is not to say it cannot be deep and loving as well (it can and often is). But you must allow it to evolve at its own pace.
Compromise is also very important. In a sense, you must now learn to share your mother or father, and this can be very hard to accept. Above all, don't sulk or try to wreck things. If you do, one of two outcomes are likely. First, you may succeed. But then what? Just think what a selfish, spiteful monster that would make you – spoiling the happiness of someone you love just because it suits you. And how do you think your parent will react? Even if they separate from this new person they may never forgive you for what you have forced on them. More likely, your tantrums and nasty comments will just create a toxic atmosphere while altering nothing.
Remember, compromising means accepting; it doesn't mean pretending to be happy. You may genuinely dislike the new person. On the other hand, you may find no faults but have to admit that you struggle to accept. To make that compromise and acceptance a little easier, be careful not to compare. As has already been said, the relationship between stepchild and step-parent is unique. It isn't fair on you or your step-parent to compare them to your biological father or mother. Again, this isn't about you. Your father's new partner has not arrived in order to be your new mother. She is in a relationship with your father, not you. How your relationship evolves is up to the two of you.
Finally, there is the question of jealousy and guilt. Many children feel a raw, burning jealousy that has nothing to do with the biological parent who has been replaced. This is especially common when boys see their mother with a new man or when girls see their father with a new woman. You do not need to have read Freud to observe this. It is especially common when there has been a long gap between the disappearance of the biological parent and the arrival of the new partner. In such circumstances, the children can assume the role of replacement. A teenage boy, for example, may become protective of his mother, taking on traditional macho roles and even being physically defensive. A girl may step in to provide the tenderness and fuss her father has missed since his wife left. And now a new man or woman has arrived to replace them!
Guilt is also very common. If a child's mother or father died, or if this new person came into their life following an affair, the child may feel a sense of loyalty to their other parent. Indeed, they may feel almost duty-bound to make life as difficult and miserable as possible – as if taking revenge on behalf of the deceased or betrayed parent. And should they find they like, even grow to love, their step-parent, this too can create a sense of guilt. But you must remember that you did not choose this. And if your other parent makes you feel guilty for getting along with your step-parent, then they are being unfair. None of this is your fault. If your mother or father had an affair, that is between your parents and the new partner. You are helplessly stuck in the middle.
There is no right or correct way to respond. And there is no typical relationship. Sometimes, the relationship is abusive and destructive, sometimes loving and enriching. More often, as the initial wariness and hostility subside, it settles into something more mundane: a relationship of highs and lows, just like any other.