I'm sure each and every one of you sometime in your life has felt like you need to go for a long run or some kind of high intensity workout to burn the calories from that birthday cake or the pizza you ate when you went out for dinner the previous night. Unfortunately many of us do that, which is the wrong mindset to have.
You should exercise because you find enjoyment from it and you love those endorphins that are released. Exercise should not be seen as a punishment or something that you force yourself to do because you overate at a meal or had a bit more junk food than usual. The same applies to eating. Eating food is not only for nourishment, but also enjoyment, so go out for dinner with your friends and family and attend those birthday get togethers.
If you are invited out for dinner, it's important to go out and enjoy the meal and not sit there counting calories or staying at home because the calories may be a bit higher than if you ate at home. Obviously if you have goals to reach it's important to opt for healthier choices when you are out, but if you want some ice cream afterwards then why not. It's not something that you do everyday and it's not like you are going to eat a whole tub of ice cream there, so rather enjoy your food and go back to eating like normal the next day.
Another thing that I often find people doing is starving themself for the whole day if they know that they are going out for dinner. This again is not a healthy mindset. It's important to nourish yourself with healthy and balanced meals throughout the day and still eat breakfast and lunch. If you know that you are going to have something that is a bit carb heavy and low in protein and vegetables, then I would recommend that you try and make sure that you have enough protein and vegetables in the morning and afternoon so that you are getting in enough nutrients.
To sum it up.
Exercise because you enjoy it and celebrate the fact that you are able to move your body
Enjoy the food that you eat. Don't punish yourself for having the odd treat, just remember to have those 'treats' in moderation.
Live happy and healthy!