How do I stop feeling anxious when my boyfriend goes for drinks with his friends?

you could try some exercises for your mind and body. For instance if you practice diaphragmatic breathing, alternate nostril breathing, or breathing in a supine position with a pillow breath (or something heavy on your stomach) you could help your nervous system to return to a balanced state. And those exercises you could google them, there are a lot of videos where you can learn how to practice them correctly. You could also exercise in a gentle way, doing yoga or walking or something that your body can handle when you are feeling anxious. Canalizing all the hormones that your body release (adrenaline for instance) due to the stress response is a good way of finding again inner balance. And finally doing some mindfulness exercises, staying present doing the activities or staying present while sitting down, it can help you avoid the train of thoughts that makes everything worse (your boyfriend with his friends drinking... and all the negative consequences you imagine around that scene).

You should try stoping for a moment and taking deep breaths in and out. After that you should then count from 1-10 and talk to your boyfriend about how you feel when he goes out for a drink with his friends. Don't go to him in an angery way just be calm and nice. Remmber that you are strong! Make sure that you are thinking before you speak when speaking with him remmber to stay positive. You can do this I know you can do it. Also you should tell him exactly how you told me that you feel anxious remmber you got this I have your back!