Before you make any big decisions I would wait until the exam schedule comes out. If your friend is getting married the weekend before an exam/practical, theres a slim chance you will be able to go. It sucks, but that's how it works. If he is getting married on a weekend that fits with your exam schedule then you should definitely go. I was pretty lucky with how some of my exams fell and was able to do fun things. When MSK starts, you are going to need your weekends to go to the anatomy lab and get tutored. Rule of thumb: weekend before an exam means you will do nothing at all other than study. If your brothers wedding falls the weekend before an exam, I would definitely make an exception. Despite what you may think, med school isn't life. Family is important. You will still pass, but don't get used to taking weekends off before tests.
You do need to accept the fact that you will likely miss out on many things and you will need to make sacrifices. There is more than enough time to have hobbies/go out/ watch netflix/ do whatever you want but your "fun time" will depend completely on your exam schedule. Don't be nervous. Med school isn't that hard. It's all about time management and sifting through all the bull shi* Good luck and enjoy your summer!