Getting married is starting a new family together. You and your fiance are a family now and you are the most important people to each other. If he says he's okay without his brother there, I'd say go ahead with the DW. He sounds like a great guy! It's hard when you're starting you're own family because you're each breaking off from your own families and you come to realize that you have to create boundaries between your new family and your old families. You have to both stand up for yourselves and say, "this is what's best for our family" in regards to holidays, relationships, weddings, funerals; essentially anything to do with family. This might be one of those instances. If your fiance is saying he's okay with it, trust your fiance to know what's best for him. And to be fair, my fiance's brother was missing his dad and other brother (who was the best man) for his wedding due to his brother's addiction. It sucks, and it can be hard, but he did move on from it. He still had a great time on his wedding day.