I honestly hate the phrase, "I can't, I'm on a diet." I think it bothers me so much because a good majority of people who use this phrase don't end up sticking with their diet. Yes, while on a diet you should be making good choices and not eating everything in sight but if you say no to everything all the time are you going to be able to maintain it?
My answer to that is no. To become a healthier version of yourself you have to find a balance between making better choices and still eating things you enjoy in moderation. You can do this is so many different ways, I am not here at all to tell you which way is the best! What works for me might not work for you! I personally found counting macros to be the best for me. I'm able to monitor and track what I eat while still being able to eat foods I love, like donuts! I was able to maintain this lifestyle while hitting my goals. I also loved that it turned into a lifestyle rather than a diet.
Every time I would start a diet I would start out strong and eventually lose steam. Holidays were hard, going on vacation was hard, going out to eat was hard! I would finally just give in and give up. Being able to be flexible with my diet was where it all changed for me. Suddenly I was able to continue my journey all while making better decisions and continued the success through the holidays and nights out!
My point through all this is that you need to find that balance in your life and diet. Cutting out everything you love is not realistic and not sustainable!