I feel you.
I too value my friendships highly, I respond promptly and if plans are made I will be there with bells on! I struggle when others don’t value friendship as much as I do. It has gotten to the point where I don’t suggest plans and any plans I make, I make sure they’re for things I’d be happy to do even if the other person flaked.
Rejection sensitive dysphoria is real and it makes us doubt our own worth when the other person simply cannot get all their ducks in a row for whatever reason.
It’s probably not about you. If you have any acquaintances in common you can ask them and they will probably tell you your friend is “just like that”
However I also know that the above doesn’t help much when your friend flaked on plans again!
There is someone who I have a blast with when we do get together but, she has flaked or been radically (hours) late one too many times. I don’t make plans with her without there being a feasible situation if she does fail to show. I won’t subject myself to the hurt. I know she doesn’t do it to be malicious…it’s just her.
I’ve been blown off by someone who does so to hurt me. I won’t make plans with her either!
I don’t think you’re too demanding as a friend. I just think the other person might just be flakey and if you can figure out what’s driving it you can make plans that won’t get you hurt…
When you honor and value friendships with people who don’t exhibit the same values it can be so painful…I’m sorry