OP-- I know exactly how you feel. DH and I went to see Ian Anderson a couple of years ago. I thought I was going to literally die-- yes literally. I wanted to go out in the lobby area so bad I could hardly stand it but I knew if I did DH would leave too. He was really enjoying the show. Afterward he knew I didn't enjoy it and has promised to accept a 'no' from me if I don't want to go to see an act. There is no need for him to spend the $ on a ticket for a show I don't enjoy. I go to concerts with friends for shows I know he wouldn't enjoy-- NKOTB
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I would tell you MIL that you aren't sure if he still enjoys that band and she may be wasting her money. If she still buys the tickets tell your husband to ask a friend. If he insists you go and it will cause a fight this may be one you have to take for the team.
I just saw the post with the name of the band. We saw them a few years ago. Really their shows aren't that bad. Yeah, some people get dressed up and all but there were a lot of regular suburban people like DH and I there too. I would start early with suggesting your DH take a friend if you didn't want to go. They actually but on a great show.