Not attend my step brothers wedding and i feel horrible help!

Okay so early March 2018 my step brother announced that he would be getting married July 2018! I thought wow that’s fast but okay they have a kid together and have been engaged for a little over a year but I never talked about the wedding since getting engaged.His fiancé never asked me to be in the wedding she TOLD me I was which I don’t care for we aren’t close and I only talk to her on holidays in passing and the occasional Facebook like,she also changed the wedding date 4 times in a week of telling us. Meanwhile I’m not the best to communicate with because I work overnight and go to college full time so I told her I don’t think it would workout with me being in the wedding I wished her and my step brother the best and if she needed help since I got married last year I’m always here if she has questions.Then I just so happened to look at my calendar and get a reminder email of a concert we have tickets to in Canada and we can’t get our money back and it cost $$$ for the concert, so I explained this to her and said I was sorry I couldn’t go. Not I feel horrible about not going to the wedding but again we aren’t close but they did go to my wedding but I told people almost 2 years in advance and the concert plus travel cost about 1200 which we have already paid for. The responses for this will probably be I’m an asshole but I needed to vent. I hope everyone has a wonderful day.