This is where lessons from my beloved Mr Montignac come in handy. The author of the excellent 'Dine out and Lose Weight', first published in 1986, Mr Montignac set out to lose weight whilst dining out everyday, and succeeded!
The full diet is too much to cover here but in essence it involves avoiding all sugar (only fruit or low sugar dark chocolate desserts are allowed for pudding) avoiding all carbohydrates with a high glycemic index (white rice, white bread, sugar, dried and tropical fruit, potatoes) and not eating any starchy foods other than pulses with a meal containing saturated fats ie any meal containing meat, cheese, butter, cream or eggs.
When it comes to drinking dry wine and champagne are allowed in small quantities, but sugary cocktails, diet or sugary mixers and beer are all out.
The Montignac Method promotes weight loss by regulating insulin production and in particular by reducing the damage of eating fatty foods by minimising insulin production when eating these foods. It also cuts out the addictive sugar and refined carbohydrates reducing the likelihood of over-eating. This means no crisps, biscuits, refined breakfast cereals and chocolate bars, but you can still enjoy a cheese board (no crackers). dark chocolate and fruit.
As for the dating scene, if you're lucky you may find a partner who has some healthy eating and exercise habits you might pick up. If you're a die hard carnivore and find yourself dating a vegetarian, instead of being horrified embrace it and try out some vegetarian restaurants.
If your new beau/belle is sporty then base some dates around an activity, play a game of tennis, go for a swim or even take up 'brunch jogging', which is Ms Haribos excellent idea of going for a run with friends motivated by the reward of brunch afterwards.