Why do I feel sick when I dont talk to my ex boyfriend?

The short answer: Oxytocin! A slightly longer answer: Love is not just an emotion - it's a whole set of reactions in your body and brain, most of them not really understood. The ones that are easy to test with science are biochemical and physiological - hormone levels, breathing, heartrate, and the like. When we fall in love, it's not only our brains and hearts that enjoy being with someone. Out whole body reacts to them. Our muscles relax, our heart rate steadies, and our stomach settles down. When we miss someone we love, the opposite happens: we get stressed, things seem more painful, and our immune system doesn't function as well. So what you experiencing is exactly breaking up: your body is used to this person, and any contact makes you feel good. Not having contact, even by talking, is coming down from a high. The good news is that it will get better if you can stay away - your body will adjust and stop being sick. It takes time, but it's worth it. Be strong

Breakups are like grief and can manifest physically. This is perhaps why we call it a "heartbreak" because our brain processes the emotional pain very similar to physical pain. It's hard letting go of people we love, even if we know we have to. Think of that sick feeling as a withdrawal symptom - love makes us feel like we literally can't live without that person. Remind yourself that you absolutely can and that these feelings, this pain, won’t last forever. Use this opportunity to focus on yourself in ways you never have before and know that healing takes time and there is no time limit or set time for getting over someone - go at your own pace.

Minds are a really powerful weapon, if you don't want to talk will find a lot of reasons not to do it. Even if could be get sick

You're missing the feeling of life as it was. You're mind is readjusting and literally changing shape to accommodate the new reality. This gives a great opportunity to a fresh start, but it will hurt when you look into your life as it was. This is natural, normal, and will only get easier with time:)