‘Your oldest friends are almost like a scrapbook of your life,’ says Dr Irene S Levine, friendship expert, psychologist and author of thefriendshipblog.com. ‘They knew the person you were as well as the person you have become, and can pick up nuances without you having to make lengthy explanations.’

So what can you do if one of you moves to the other side of the world?

1. Commit

Make time to pick up the phone, email or text to keep up with each other’s lives. ‘The precise frequency of contact varies from friendship to friendship, but you need to discuss this and re-negotiate it over time,’ says Dr Levine. ‘It’s important that you recognise milestones such as birthdays, anniversaries or promotions, and show support through difficult times such as a loss or divorce.’

2. Personalise

Social media is great for keeping in touch, but find new, more personal ways of communicating. An old-fashioned letter or a photograph of you both from your teenage years will go a long way to make your friend feel special. ‘Talk about the ways that work best for you both,’ advises Dr Levine. ‘For example, it may be that one of you hates Facebook or feels uncomfortable receiving messages at work.’

3. Create new memories

‘When it comes to properly maintaining friendships, old memories won’t suffice,’ explains Dr Levine. ‘Friends need to create rituals to build new memories together.’ You can try visiting the same restaurant or café whenever you see one another, or perhaps invest in a shared holiday at a midway point between your two countries.

4. Focus in

Show that you’re interested in your friend’s life by asking about her kids’ school, her social life and even what she had for lunch! The intimate details often count for more than the bigger picture.

5. Be honest

‘Acknowledge that you spend less time together, or that there’s a void, or that your relationship has changed,’ suggests Dr Levine. ‘And help each other adjust.’

Photograph: iStock