The other day I had lunch with a very old friend. But actually calling her a 'friend' isn't really accurate – she is more of an 'ex-friend'.

I have known her most of my life – if not all of it. When we were young children I didn't like her very much. She was a rather precocious only-child who would threaten to set her dogs or father on me if I didn't do what she wanted. In hindsight, neither the dogs nor her Dad were particularly scary but my six year-old-self was still terrified enough to comply with her wishes.

Her behaviour towards me improved with age and so did our relationship. By the time we were 12 we were close friends doing what teenage girls do: we hung out, partied, went on holidays with each other's families, discussed boys, shared confidences, enjoyed pushing boundaries, dreamed of the future and planned how we would make each other godparents to our children if and when we had them.

We were in our early twenties when our relationship drifted. I have often looked back and wondered why. It wasn't as if there was a big row or one of us wanted to re-invent our selves. It just happened. In my more insecure moments I would ask myself if I'd been a bad friend? Did I say or do something to push her away? But I think the truth was more mundane and possibly to do with us wanting very different things from life and moving in different circles.

Most of us probably have a few friendships that only lasted for a season. That's natural – after all there's a limit to the number of friendships we can maintain. Professor Dunbar, an anthropologist from Liverpool University, discovered that on the whole we humans have the brain capacity to cope with a social network of up to 150 people. Those are 150 people whom we know, relate to and would be happy to join for a drink if we bumped into them unexpectedly.

The number is considerably smaller for close friendships. We can only deeply care for around 12-15 people at any time. Perhaps, it is no coincidence that Jesus chose to have 12 disciples.

But how do we decide which friendships to invest in and which to let go? And if a friend decides to dump us – against our wishes – how can we respond?

These are questions I have and am still wrestling with. But let me share a few thoughts on how we can navigate the difficult terrain of friendship break-ups.

1. Communicate

If you sense something going wrong in a friendship – communicate about it quickly. Small things can build up and it helps to voice concerns when we have them rather than just worrying about them in our head. Often conflict is born of a misunderstanding so if we can air the issue – it might prevent the problem escalating. It always helps to be open to feedback and to apologise for our part if we have done something wrong.

Ideally, talk to the friend involved first and not to other people, especially if they know you both as this often just causes greater upset.

2. Remember friendship is a choice

Friendship is freely given but it can also be freely taken away. There is no family bond, marriage commitment or employment contract holding friends together.

If a friend chooses to distance themselves from us or to break off all contact, that is their choice. We can ask for an explanation but we may never discover the real truth. It could be that their reasons for moving on are nothing really to do with us – and more to do with them and something they are experiencing or going through.

If we have done our best to communicate and to apologise for any wrong on our part (if something we did was the problem) then there comes a point where we just have to respect their decision.

If we are the one ending a friendship, it can help to think – how would I want to find out or be told about it?

3. Be intentional

Some friendships just drift slowly apart – perhaps as we move cities or during a certain transition in our lives. If we are worried as to what will happen to a friendship or don't want it to end – it can help to voice our expectation or concerns to our friend.

It is important that we are intentional about investing in the relationships that we do want to survive even if it means working out together what that friendship in a new season might need to look like.

I used to meet regularly with five women but when I moved cities two years ago I could no longer join them for their monthly get-togethers. However, I still really value those friendships so I try to be intentional about arranging to see them and I make an effort to join their suppers at least once a term.

3. Grieve

When friendships change or end it can help to acknowledge this and grieve the change. Grieving helps us to work through any pain or disappointment and 'let go' of what is no longer. We will still have our memories. It doesn't change the past – it just means finding a new normal for today.

4. Pray

When I have struggled to understand the shift in a relationship or the sudden disappearance of a friend, I have found it really helpful to pray. Jesus knows only too well the betrayal of a close friend and it can help to seek his perspective and healing for our own situation.

5. Keep the door open

I think it is rare that a friendship has to be cut off completely unless the relationship has become abusive or toxic.

In most cases in my own life I have kept the door open. This has been particularly true in situations where I wasn't the one who pulled back.

I believe the best option is to provide a simple opportunity for re-connection: an invitation on Facebook, a Christmas card or text message. The secret is not to force anything or to expect too much.

If they don't want to reply or re-open the relationship then we have little choice but to respect their wishes. If they do – we need to be prepared that it might only be for a quick reminisce. A past history of friendship is, after all, no guarantee of a future one.

6. Nurture other friendships

When we prune back our rose bushes in the garden it allows for new growth. When friendships end or are scaled back – it creates more space for us to nurture other relationships. I wonder if it is worth asking – which friendships do we want to deliberately nourish and nurture in this season?

In the end the lunch with my former friend was her idea. Being with her felt reassuringly familiar and easy. Will we pick up the threads of friendship again now we have re-connected? I'm not convinced. However, I will always have very fond memories of our past friendship and I would happily say 'yes' to a coffee and a reminisce every now and again.

Sarah is Abell is an author and relationships coach. Her passion is helping people live, love and lead more authentically. You can find out more at nakedhedgehogs.com