It’s already been answered but yes, it is breaking your fast and is not allowing you to get the most out of the work you’re putting in.
The reason I want to post is that I was once like you with coffee. I couldn’t start my work day without it and definitely had withdrawal headaches when I quit. To compensate I turned to tea. Now before you tell me tea doesn’t do the same for your body as coffee, I felt the same way. But I went and got some great ginger tea. It has no caffeine, has a strong taste, and is a digestive aid. It helped me pivot away from coffee entirely and eventually I just stopped drinking the tea. Now I go for a big glass of cold water in the morning and, if I want to have a cheat day, I can have a cup of Starbucks or sugary coffee for fun here and there without getting reattached to it.
Best of luck! True 16:8 fasting will make a huge difference in your life!
Yes, the sugar will break your fast.
It would be better to have a teaspoon of heavy cream and no sugar — less of an insulin spike. Still considered a “dirty fast,” but many do it that way and successfully lose weight. (I did it that way until I decided to re-try black coffee and found out I liked it!)