Family Friction: When Stepparents Cross the Line

Navigating Boundaries with a New Stepfather
Last year, my mom remarried, and her new husband, Ken, has quickly settled into our family dynamic—perhaps a bit too comfortably for my liking. As a 26-year-old adult, I'm finding myself struggling with the sudden shift in our household's balance and Ken's increasingly intrusive presence.
While I understand that blending families can be challenging, I feel like Ken is overstepping boundaries and trying to establish himself as an authoritative figure in my life. His well-intentioned but often unsolicited advice and constant attempts to insert himself into my personal affairs are becoming increasingly frustrating.
I want to maintain a respectful relationship with my mom's new husband, but I also need him to understand that I'm an independent adult who doesn't require constant guidance or intervention. The delicate dance of establishing healthy boundaries with a new stepparent is proving to be more complex than I initially anticipated.
How can I communicate my feelings effectively without causing unnecessary tension or hurting my mother's happiness?