Our actions 'teach' others what we will or won't do....
Our actions 'teach' others how far they can push us...
Our actions or in-action creates within us our own self image.

People don't want to get dumped.
Your Truth, they no longer serve a purpose in your life.
Create Boundaries of what you will and will not accept from your friends, and use kind with words. There will be less hurt feelings.

Until then nothing will change, they are your emotional vampires. I suggest Alanon to help you get through with support from others where you are now. I've been in a similar place as your 'friends' in not wanting to loose a 30year friendship....back and forth for nearly a year....finally I just accepted that the problem/issues were something my friend needed to work out for herself....I just said OK And haven't seen or heard from her since...and that's ok....I Sincerely Wish Her Well...still love her dearly as a friend and if she were ever in need I'd be right there to help her....she's in my heart.....That Doesn't Mean I Would Go Back To Being A Friend on a continuing basis....I would respect what she wants.

When you just back off your friends don't read your mind....and may or may not know how you feel.

I see that knowing you are not going to go get that book is setting a boundary. The real way we set boundaries is to decide what we will accept and not accept from others. So you already know you won't accept going to get the book. Perhaps you. need to learn a few handy phrases to use when getting these calls. Or don't answer their phone calls or block them. If you feel you simply can't tell someone "I gotta go... so bye" then figure out a few phrases and write them down on paper and practice them. I have said, "The doorbell is ringing" or even "I gotta go to the bathroom" and then cut it off. Don't wait for them to cut it off, they will keep talking. If this is the boundary you need to learn, then practice doing it. And then actually do it. We don't have to respond to text messages either or we can say sorry too busy right now to respond. So yes, you can stay a rubber band and allow people to pull on you or you can decide no more. My trick is to think up some tactics I will use. One of them for me was learning so say no when I feel like no. I recently had to say no and enjoyed my own power. Think of it as being your own best friend. Do not allow anyone to rubber band you. This is sort of setting boundaries but it is mostly taking back your own internal power and doing what is best for yourself instead of yo yo-ing from someone rubber banding you. And yes, when you get stronger, people are going to test you. So be ready. The nefarious ones want to pull you down and manipulate you. The users just want to use you. Like I already said, write it down on paper what you new actions or tactics will be. Read this paper daily or 10X a day if needed. Then take a pause when the manipulators call you or text. Do not answer immediately. Don't answer the door if they just show up. Or answer and say you can't let them in as this is not a good time. Then shut the door and lock it and move away from the door so they can't hear you. Just be assertive because you are worth taking care of. Remind yourself daily that you are worth taking care of and you will no longer give away your power. Don't be as old as I am, grandmother age, before you learn this stuff. Big hugs to you.

Oh and another thing. These prompts well -- simply don't respond. And it is normal when there is a lull in the conversation for someone to jump in and fill the silence. You don't have to agree that you want the book. My saying is simply "interesting" and nothing else. Part of starting to hold yourself within your own internal "power" is holding yourself within your own internal power. Knowing that you no longer want to be prompted or rubber banded. Being okay with not being approved of or liked.

I’ve been also learning boundaries. I related a lot with the rubber band analogy. I’m a very shut down person when I know my limits. I’ve learned to turn off my phone and take time to center myself and focus on myself verses trying to people please others. It’s hard because sometimes the “others” will take it personally and shut me out in the process but. Like I saw in some of the other comments, people who understand and respect you will and won’t push you away or ask to much of you. They will indeed rationalize the situation and give you support in however they can. I’ve learned the hard way with boundaries that not everyone’s intention in your corner is to actually be in your corner. (If that makes sense) I recently just accepted my generational learned codependency and I’m breaking a cycle at 27years old. Most of my family aren’t as receptive in understanding codependency so they chose to minimize my shadings but still want me to drop everything for them mentally, physically and emotionally. But the boundary I had to embrace is.. I can’t pour from an empty cup.