There’s a difference between setting a boundary and trying to control people. Once you can distinguish between the two it gets easier.
Boundary - what I will or will not do.
Control - what I want you to do or not do,
So in your examples, the boundary is that you’re leaving at eg 2pm. At 1.50
you’re getting your coat on, and whooshing everyone out. You’re not relying on anyone else to remember or be considerate. If they’re not ready to go, then they’re locking up because you’re gone.
cup of coffee - absolutely you’re going to get interrupted (he’s 9), “I’ll be with you when I finish my coffee”, and stick to your guns, Keep it calm, pleasant and don’t escalate. Eventually it will sink in, but it’s up to you to. maintain the discipline of the practice. Be realistic - you’ll probably need about a thousand goes before it sticks. That’s ok.
Even though it’s simple and clear cut, in practice it feels entangled when you’ve been a people pleaser, and you probably have a huge need for validation and support. This is your work to do - this is how you build discipline. You need to work on letting go of the idea that it’s other people’s fault.
You don’t need to be sharp, or mean or snappy. In fact it’s way more effective not to be. just be consistent, and a broken record. Say what you mean, mean what you say.
If you have a few minutes to yourself, try this exercise: sit still, eyes closed and don’t move for 1 minute no matter what. Ignore the itchy ear, the weird feeling in your left knee that makes you want to shuffle, the sudden certainty that you left the iron on, the email you forgot to reply to, the dentist appointment you meant to book 4 months ago. Each time you feel the urge, breathe it out. It’s a fantastic practice to help you find your edges - where you end and the world begins,
It’s not easy op. But the more you do it, the more solid become.