The question of whether time apart from an ex-partner can reignite old feelings is a complicated one, and the answer can vary depending on the individual circumstances of the relationship. However, there are a few reasons why some people might feel more strongly about their ex after spending some time apart.

One possibility is that distance allows people to reflect on their past relationship without the distractions of everyday life. When we’re in a relationship, it’s easy to overlook the things that initially attracted us to our partner. But time apart can give us the space to think about what we miss about them and what we appreciated in the relationship.
Moreover, absence can create a sense of nostalgia and longing for a past relationship, even if the relationship was not particularly healthy. Our brains tend to remember positive experiences more vividly than negative ones, which can lead us to romanticize our past relationships and forget the reasons for the breakup.
Another factor is the role of dopamine in our brains. Dopamine is associated with pleasure and reward, and it plays a significant role in our experiences of love and attachment. When we’re in a relationship, our brains release dopamine in response to our partner’s presence and affection. However, when we’re apart, our brains can still release dopamine in anticipation of seeing them again. This can create a sense of craving or longing for the other person, which can intensify our feelings of attraction and attachment.
It’s worth noting that not everyone experiences a sense of longing or fondness for an ex after a period of absence. Some people may feel relief or closure after a breakup and may not have any desire to reconnect with their former partner. Additionally, the reason for the breakup and the amount of time that has passed since the breakup can also play a role in how someone feels about their ex.
If the relationship ended due to irreconcilable differences or serious issues, it’s less likely that absence will make the heart grow fonder. In these cases, the negative memories and emotions associated with the breakup are likely to outweigh any positive feelings that may arise from a period of absence. On the other hand, if the relationship ended due to external circumstances such as distance, timing, or conflicting life goals, absence may create an opportunity for the couple to reconnect and explore whether they still have feelings for each other.
In conclusion, whether or not time apart from an ex will make the heart grow fonder is a complex issue that depends on various factors. While some people may experience a sense of nostalgia and longing for a past relationship, others may not. The reasons for the breakup and the amount of time that has passed since the relationship ended are crucial factors to consider.