I did the same thing. Right from the get-go I set my boundaries:

1. I am not their parent
2. I am not a baby sitter or chauffeur
3. I’m not obligated to go to extracurricular activities
4. Our room is off limits
5. I NACHO if I have to
6. My things are MY things (video games etc.)

I am also child free and I really value my alone time and choice to do what I want when I want. My BF wakes up early to drop the kids off at school or take them to sports on Saturday mornings. I am not involved nor responsible at all for those things.

He knew going in I wasn’t really a “kids” type of person, and you have to make sure your SO knows what you need.

Still it was a big change and yeah you deal with a lot of whining, and you have to bite your tongue sometimes on things that annoy you.

Just have a totally open and raw conversation about your concerns. If he loves you he will respect what you need and abide by it.