Until recently Elizabeth Day wasn’t simply passionate about friendship, she was addicted to it. This isn’t just a figure of speech. She describes a physical and emotional dependence so strong that it had her pursuing platonic relationships to the point of damaging her own physical and psychological health.

I am a recovering friendaholic too, and I found this book, which to some might seem niche or contrived, essential reading. Being good at friendship, which is not quite the same as being a good friend, is a core self-belief that many of us (often women) cling to as evidence that we are, in some important way, both lovable and likable. Romantic partners may come and go, but the ability to tell yourself that you have a lot of friends, some dating back to kindergarten days, is a psychological lifejacket like no other.

But, as Day explains in this admirably candid and well-crafted book, there is nothing more soul-sapping than clinging to a friendship with someone just because 20 years earlier you sweated in the same spin class. For some reason, probably to do with your own fear of abandonment, you carry on going through the motions with what Day dubs “White Wine Wednesdays”. Those are the midweek get-togethers (neither of you would dream of giving up a Saturday night to each other) which are somehow never as nice as they should be and leave you feeling down, depleted and as if it is somehow all your fault.

Yet you persist with the friendship, driven by the belief that letting it fade would be pretty much a crime against humanity. Less melodramatically, it would also show you up to be the things that you’ve always fought so hard not to be: fickle, unreliable, selfish and, most of all, alone. What, though, could be more selfish than hoarding bad friendships? It means that you have less energy and time for the people you want to be with, the ones who deserve you. Or, as Day’s friend “Sathnam” puts it, hanging on to friends you don’t like is hardly a compliment to the people you do since “it means you’ll be friends with anyone who’ll have you”.

To buttress her deep dive interviews with friends and a friendship coach (yes, there is such a thing), Day mines the research literature – which is pretty scanty. There are a few standout points, though. Apparently having four to five close friends is ideal. If you have more than seven then you are likely to suffer exhaustion from trying to juggle everyone’s needs. Studies also tell us that we replace half of our friends every seven years. This pruning is natural, healthy and necessary. So if you are still, as Day was at one point, determined to maintain every friendly connection you’ve ever had, it is an index not of your niceness but of your desperate need to hang on to several skips’ worth of emotional lumber.

Having seen the light about her past self-sabotage, Day is determined to be ruthless in the future. She suggests, not quite jokingly, that it might be a good idea to send potential friends the equivalent of a pre-nup before agreeing to a first coffee date. On this document (you could have it laminated) you would list what you can and can’t offer a new person in your life. Mine, for instance, would explain that I don’t do phone calls but I will answer texts immediately. That I prefer cinema dates to ones in bars and that I don’t do hugs (it’s nothing personal, I just don’t). I am bad at birthday cards but good at emergency call-outs. My preference is for once-a-month meet-ups with an option to consider a mini-break in Prague if things go well.

It sounds preposterous, but it would save a lot of White Wine Wednesdays further down the line.

• Friendaholic: Confessions of a Friendship Addict by Elizabeth Day is published by 4th Estate (£16.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply.