it does feel so... different.’ Better is what they mean. Better than what you have, you poor unmarried, unofficial creature.

I’ve seen it happen to other perfectly sane women. There seems to be some prided pleasure in conforming to a stereotype – she can’t come for drinks because she has to get a casserole in the oven. And as a walking, living brand, bonded by wedding rings and decorating ideas, the two of them now do everything together. What if Tom suddenly wants in on our wine and Glee nights?

Even if they don’t succumb to all of that, their relationship will, with an ‘I do’ and a kiss, become a more permanent and mature version of what I have with my boyfriend. Marriage is usually setting the stage for the most permanent thing: babies. Should Kirsty fall pregnant next year, everyone will assume that it was planned, that, in fact, the marriage merely signalled that her uterus was now open for business. If I were to fall pregnant, people would wonder, not entirely without reason, why I’d been so slack with the contraception.

Partly it’s the practicalities. What if they move far away to the country to raise kids? What if I can’t stay in her spare room any more because there’s no space for me, with the Moses basket and mobile and everything? What if she can’t drink wine?

Then, partly, it’s a less tangible thing. It’s the fear that she’s moving on to the next stage of her life and I’m lacking the pass to cross with her. Because she’ll be a wife. And with that term, society awards you a level of respect and responsibility. There are tax breaks and the assumption you’ll post a birthday card on time.

What if all the stuff that has bonded us until now – our love of travel and karaoke and caramelised onion marmalade – can no longer sustain us? What if all of that is swallowed up by simple wifedom? She will be something that I am not. Worse, she has other friends who are that thing, who’ve experienced that life shift. It’s probably starting already. They’re handing her numbers of caterers and florists. Whereas the only wedding advice I can proffer is, ‘A free bar is always good.’

And they’re not the only ones chipping away at your friendship because, really, that starts the moment he walks into your lives. With all that romantic, everlasting love, he trivialises what the two of you feel for one another. Friendship is the only sort of love that has no standing in society. It doesn’t grant you access to a hospital room. It doesn’t make mournful missing persons appeals on TV. It’s not an

emergency number or a plus-one. As far as onlookers are concerned, you’re a mere bit-player. And that’s just not fair. Because, in most cases of best friend versus boyfriend, you were there first. Where was he during the acne and braces years? Or when you had to pick her off the floor during those early – and then later – heartbreaks? Did he spend endless evenings learning the words to the PJ & Duncan rap? No.

For years you have been each other’s constant. It was the two of you sharing the laughs and the tears. It was each other you’d turn to first, just a phone call away if you were needed. And no matter the ebb and flow of the friendship and the side alleys life nudged you down, you’d always come back to one another.

She has been your life’s keystone. And you hers. Until, by way of an engagement ring,

you’re suddenly not any more. Because here he is: Mr Latecomer. In all his husband-to-be glory. What about us? Is ‘us’ now less important than ‘them’? And then it dawns on me: not less important (I hope), but just less obvious.

So, as Kirsty’s wedding draws ever nearer, I’ve decided to tell myself this: friendship, just like the rest of life, is a constantly changing thing. Though the essence of what connects you may remain the same, the relationship will constantly reinvent and remould itself. And you can’t freeze it in time at a supposed heyday, clinging to the shards like an old woman mourning her lost beauty. You can only embrace it, love it and move with it, celebrating each metaphorical laughter line along the way. That’s the way not to be left behind as your friend moves on.

Besides, it’s not just you who’s scared. ‘What if I get married and you just assume I’m going to spend all my time with Tom and never think to invite me on holiday or on a mental girlie night?’ Kirsty panicked over wine recently. It would never happen of course. I need her to go and get the crisps for a start.

You can only promise each other what you’ve always promised each other – that you’ll always be there, that nobody will take her place. Because she may be someone’s wife but she’s still your best friend – and even if it’s only the two of you who understand how fundamental that is, well, that’s enough.

As Annie assures Lillian in Bridesmaids when the bride is having her own meltdown on the morning of her wedding, ‘Things are going to change, but they’ll be better...’ So pour another glass, look forward to what the future may bring – and beg her not to put you in peach. Bridesmaids is released nationwide on 24 June.

‘What if her husband suddenly

wants in on our wine and

Glee nights?’

Lillian The BRIDeShe gets on with everyone – so the five friends she brings together as her bridesmaids have nothing but her in common.

Annie The SIngle OneEssential to remind you that there is life beyond marriage. You will now be living your life vicariously through her.

Rita The CynICal OneAfter several years of marriage, she has a dim – make that downright scornful – view of love. Scary yet informative.

Helen The PeRfeCT OneBeautiful. Successful. Rich husband. Will organise everything. Will also look better than you in photos and make you feel inferior.

Megan The KOOKy OneShe’s a complete one-off, and that’s why you love her. Within her weird world view are cloaked words of wisdom.

Becca The Smug-maRRIeD OneProof that smug-married is not just a stereotype, she happily indulges your ridiculous romantic side.

Aisle be there for youIn chick-flick Bridesmaids, above, the ladies are as colourful as their dresses. So, who would be your wingwomen?