Let me start with the bad news. You can't stop your girlfriend smoking . Any more than you can stop your girlfriend eating chocolate, watching reruns of Friends, shopping, gassing on the phone or calling you "Chubbachops".

A woman does what a woman decides to do. That's not meant chauvinistically. A man does what he wants to do too. The point is this: nobody can make anyone do anything against their will unless they use force or leverage. And if this relationship is important to you, force or leverage aren't things you want to entertain.

So while it's OK for you towantyour girlfriend to stop smoking, drop any idea aboutmakingher quit.

Top of the agenda is for each of you to talk about your feelings on the subject. You, however, have to exercise a little restraint. Don't start using words like emphysema and chronic obstructive pulmonary disorder. Or reminding her that cigarettes contain more than 4000 chemical compounds and 400 toxic substances. Or emailing her jpegs of cancerous lungs. Smokers are well aware of the facts – or else they choose to ignore them.

Let her do most of the talking. You may be surprised. She may have tried quitting before. She may even have given up for a while and then started again. This is all useful information. You'll learn a lot about the kind of person she is and what her triggers are.

Chances are she's far more sensitive about being in a relationship with a non-smoker than you realise. And it won't have taken her long to figure the reason you're having this discussion is because you want her to quit. So be aware of how it looks to her. However tactful you are, there's no mistaking the message. You're letting her know that you'd feel a whole lot better about her if only she had the willpower to give up the cigarettes.

Trouble is, if she's tried in the past and failed, she'll be extra nervous about trying again. Because if she fails this time, she'll be letting you down, putting the relationship at risk and creating a negative self-image.

If you're starting to feel a little helpless at this point, don't. There's plenty you can do – and plenty you're already doing. First, she'll appreciate the simple fact that you're listening to her instead of lecturing her. As long as she's open to the idea of quitting, she'll know from your sympathetic approach that she can count on your support and encouragement. Any challenge is easier if it's shared.

The decision to quit is, however, only the beginning. Next she'll need to decide how she's going to go about it. Patches and gum are popular choices. But one alternative that more and more smokers are turning to is electronic cigarettes . Like patches and gum, electronic cigarettes – also known as e-cigarettes – continue to meet the smoker's need for nicotine.

It's important to understand just how addictive nicotine is. Once you take this on board, you realise why smokers have such a hard time quitting. Nicotine acts directly on the brain. It mimics a neurotransmitter called acetylcholine. Every suck on a cigarette produces a surge of acetylcholine. This triggers a rush of dopamine, which makes the smoker feel good. Once the brain has gotten used to having a regular dose of nicotine,  it comes to rely on it. Stop the supply and your body chemistry can't cope. You don't just stop feeling good, you start feeling bad. Real bad.

Most non-smokers know next to nothing about how patches, gum or electronic cigarettes work. If you want to help your girlfriend choose which route to take, you might like to do a little research yourself. She's sure to appreciate it. She won't feel she's tackling this on her own. And that single fact could be the difference between her failing and her finally managing to quit. Imagine what that could do for your relationship.