I feel like a horrible mom

I have a 10 5 and 1 year old and ever since it was time to go to the dentist my kids have gone every year or what ever it is 6 months or so? anyways we have a pediatric dentist we have been going to since my oldest was a baby.. he's old so he doesn't do any major surgeries any more if there's a case he will refer to another Dr. which we had that situation with my 5 year old about 2 years ago. so about a month ago I figured we would switch dentists because I know our dentist is going to end up retiring soon so my 5 year old was due.. we took him Friday and when the dentist looked at his x ray she was like ur son has severe decay he's going to need 6 crowns and 1 extraction. I almost passed out I was so in shock. A. because I've been taking him regularly and there hasn't been any issuesl since 2015 and B I look at his teeth regularly there's so major dark spots just a few minors things he never complains and brushed twice a day. I started crying in the office they said it's very important u get him in right away. they want to do everything in 1 day and cant get him in until end of nov. should I get second opinion? should I take him to where he originally goes and act like I don't know anything? I feel awful.. please help