My mum met my now stepdad when I was 13. We did clash, mainly because I was a bit of a selfish arsehole, and I resented someone else taking my mum's time. I moved out when I was 17, but moved back for a year or so in my early 20s.
I'm in my 40s now, and have a family of my own. I love my stepdad more than my bio dad. If my mum had broken it off with him because of me, she'd be so lonely and unhappy, and I'd never forgive myself for that.
My mum has a son from another relationship, and my stepdad adopted him as his bio dad wasn't interested in him. My brother is autistic and has mental health problems. He's in his 30s, but has spent most of his adult life living with our parents. He got married once and lived with his wife. They divorced eventually sadly. He's now living with another girlfriend and her family, but he does struggle.
DM has coddled him over the years and he's become accustomed to having lots of things done for him. We know DB will be back home at some point though. And I know DSD struggles. Throw in the shit I've given them over my life as well, he's put up with a hell of a lot.
I would never be disrespectful to him, and if my DB is, my mum will always pull him up on it. DSD is a good man that doesn't deserve that.
Also... all families bicker at some point, whether it's a traditional family or a blended family. It's certainly nothing worth moving out or ending a relationship over.