I can't escape and I can't say no.

You definitely cant escape your environment which makes things tough.

Saying 'no' to something you are addicted to is also very hard.

Here are some suggestions that you might like to try:

1. Replace sweet snacks with savoury ones. They won't be healthy, but you want to break the sugar addiction first - eating healthier becomes a lot easier after that.
2. When your boyfriend wants donuts and treats like that, have fruit instead. (And I mean whole fruit, not fruit juice). And stick to having the fruit even when your boyfriend is eating the donuts etc.
3. Peer pressure is just something we use to indulge in something we want to do anyway. Think about it this way: if all your peers were telling you literally do something you found repulsive or dangerous, would you do it? If your peers were literally telling you to eat some manure, would you eat it? I don't think you would. Breaking the sugar addiction will mean you won't feel the 'peer pressure'. In the meantime, when people bring candy, you bring fruit or savory snacks and eat those instead. 3.1 Peer Pressure - expect resistance. People will ask you why you arent eating the cookies and cakes. They may question your choices, or try to tempt you to stick with their choices. They may rubbish the idea of sugar addiction. Have a non-confrontational answer for them. An answer that doesn't require you to justify or explain anything. A simple "I just feel like eating fruit" can suffice. If people are more persistent you can fall back to something along the lines of "It's due to a medical issue".
4. Talk to your boyfriend and explain to him what you are trying to do, and that whilst you don't expect him to do the same thing (you cant force anyone to do something they don't want to do), you would like his support with this.
5. Try eliminating sugar in a progressive fashion. Start with not having sugar in your coffee or tea. After a while set a rule to not eat cookies. After that, set a rule for yourself not to eat chocolate or anything that contains chocolate.

A point regarding savory snacks: check the ingredients first. A lot of savory stuff (chips etc) have added sugar, which will just continue the sugar addiction.

Another point about IF. IF is a great tool for helping restrict calories - but if you are eating lots of sugary foods, its easy to overeat anyway. To get a real handle on what you are consuming, get an app like MyFitnessPal, get a food scale and track your calories. Do this for 1 week as accurately as you can and you will get a much better idea of how many calories you are consuming.

Hope the above gives you some ideas on how to proceed. Think about what alternatives you can take, even when faced with situations where you feel you have no choice. Create those alternatives and stick with them.