If you want to show any compassion and retain any respect, deliver the news in person.
Diamonds are forever, but most relationships aren't diamonds. Chances are that you will dump and be dumped at least a few times in your life, and neither experience is pleasant.
But if you've lost that lovin' feeling, breaking the news is a chore that's got to be done, and it's worth doing right.
We've all heard about those inspirational couples who fell in love at 16 and remain blushingly besotted 50 years later. That's lovely. But many relationships, are not like that.
Here's our 10-step damage-limitation strategy for saying goodbye.
1. Don't rush into it
The dating game is a minefield of greener grass, especially online. It's all too easy to get addicted to the buzz of a new admirer, mere weeks after you met the person you thought was perfect - and to whom you promised the sun, the moon, the stars and a house in the country. Now you've gone off them because there's a better prospect in your inbox, and anyway you saw them pick their nose.
Before you abandon reality for your latest cyber-babe(s), make sure the trade-off is worth the risk. Novelty always wears off. If you fear the relationship is getting too heavy, talk before you dump - you may find that your partner also wants to slow things down.
2. Don't drag it out
Breaking up is hard to do. You may be leaving someone you care about and dreamt big dreams with. But the short-term pain of a break-up is infinitely preferable to years of unhappiness in an unfulfilling relationship.
If you are convinced that you'll never be happy with this person, don't delay the inevitable. The sooner you break the news, the sooner both of you - especially your rejected partner - can mourn and move on to a better match.
3. Don't go AWOL
The "disappearing man" strategy (sorry chaps, it usually is men) is the most offensive and hurtful means of extricating yourself. You may decide that cutting all communication overnight is the kindest way out. Kinder for you, maybe, but it's fantastically painful for your dumpee, who will blame herself, never get closure and may never trust a suitor again. Well done, brave man.
Incidentally, disappearing for a while before resurfacing with a brief email to say "just so you know, you're dumped" is almost as bad. However it does at least give your dumpee something to print off and burn on the barbecue.
4. Do it in person
If things have never progressed beyond the internet or first date, it's fine to end it with a courteous email. But if it's gone further, especially if you've declared serious intentions, met friends or become intimate (yes I mean got naked), email is a cheap and cowardly way to end it - and so is the phone.
5. Do it at their place
Don't ask your soon-to-be ex to meet at your place or in town. You'll just condemn them to a miserable journey home. Being stared at by 1,000 commuters whilst weeping on the train does not aid recovery, it's just humiliating. And let's not even talk about making them drive home.
What's more, delivering the news on their turf shows that you value their feelings enough to make the journey. They're on familiar ground and empowered to respond in whichever way gives them comfort: throwing you out and slamming the door; running to the kitchen for Haagen Dazs; wailing in bed for 12 hours. If you're very lucky, they may even be relieved and offer you a beer.
6. Be honest
A relationship rarely fails because someone's done something wrong. It's because the two of you aren't compatible enough to work it out. So don't go slinging blame around.
Explain as much as you can about your feelings without making the other person feel inferior. You don't have to tell them they're sexually unattractive and crap in bed, but do avoid falling back on "it's not you, it's me", which is old, tired and meaningless.
Even if the break-up is motivated by their behaviour, such as continuing to date online behind your back, first make sure there's not some innocent explanation. Then simply communicate to them that the relationship doesn't meet your needs or expectations. Hold on to what was good in the relationship and tell them that. Don't pretend it was all bad.
7. Let them talk
Goodbye should be a discussion. Allow your dumpee to have his or her say. It's human nature to want closure, so don't expect them to shrug and accept the news without an explanation, especially if it has come out the blue. Be ready to hear and to answer "why?"
Make sure that your reasons are about you, not them. Otherwise they'll beg for a chance to change. If it's about you they've got less opportunity to make you change your mind. Just say something like, you've got a gut feeling that you're not going to work out in the long term, and you really need to say goodbye.
Don't get into a battle. If you really do want out, stick to your decision.
8. Don't beat yourself up
Just as you shouldn't blame the other person for everything, don't blame yourself either. Acknowledge what you contributed to the break-up, but don't shower your dumpee with a vat of self-loathing. You deserve to walk away from this with some dignity, too.
9. Don't ask to be friends... yet
Don't end the conversation by asking your ex to come to the pub on Friday, but just as friends. It feels like a demotion, even if you started out as friends initially.