Should I go to my boyfriend's sister's wedding?

So I was going to put this long thing on here about seeing how your boyfriend feels about it, then I got to thinking, I'd just suck it up and go. Not for his sister, but for your boyfriend. I mean, I know I'd be not thinking long term plans with a guy who didn't want to come to a wedding I was in. I would probably be hurt. I know I'm not a guy, but it would bother me. It's just one day. I'm sure you can handle it. and if you and the bf are serious, it would be a great moment to show your dedication to him and that you want to be a part of the family.