To determine the key factors, the researchers first asked 348 volunteers to list the reasons they would consider staying friends with their exes.

This led to an overall list of a whopping 153 reasons, which were then whittled down to seven by being ranked in importance by hundreds of other volunteers, who also had to complete personality questionnaires.

After all this, the researchers finally identified the following key motivators:

Reliability/sentimentality (e.g. “They were a great listener.”)
Pragmatism (e.g. “They had a lot of money.”)
Continued romantic attraction (e.g. “I still had feelings for them.”)
Children and shared resources (e.g. “We had children together.”)
Diminished romantic attraction (e.g. “I realised I was no longer in love with them.”)
Social relationship maintenance (e.g. “To maintain good relations with their friends.”)
Sexual access (e.g. “To keep having sex with them.”)

Of all the reasons, reliability/sentimentality were rated as the most important by the participants, while practical reasons, such as those involving money, were rated as least important.

This is why you stay friends with your ex, according to science