Time and space are key ingredients.
When in the throes of new love, people often want to move quickly and often move in together too quickly. However the complexity involved in blending people’s lives who are connected by 1° of separation (such as being my partner’s child, or my dad’s girlfriend) means that they require lots of time and as much physical space as possible to help them get used to the transition. Children can often be emotionally confused and conflicted and need their parent’s reassurance and time to support them in embracing their new life (which they often do not). If children are only seeing their parents on scheduled visiting times and this time is also being shared with a new partner, it can lead to a lot of heartache for children, the feeling of rejection, jealousy and anger. If the co-partner is trying their best to get along with the child, which is often interpreted as being overbearing or being intrusive on the parent-child relationship, this makes the space very claustrophobic turning the situation into a pressure cooker. Time and space allow for some of the built up steam to blow off.