Expectation is defined as:

the feeling or belief that something will or should happen

Expectancy is:

hoping that something, especially something pleasant, will happen or be the case

For me, a healthy relationship has plenty of expectancy and no expectation.

Expectation leads to resentment as soon as someone doesn’t fit the mould of how you are or how you expect others should be. It inevitably leads to some level of attempting to control things external to you, and creates resistance to reality whenever it doesn’t match up to your preconceived views of how other people should behave.

Expectancy is respecting your own boundaries and other people’s. “This is how I’d like things to be”. And then they can do what they will with that information. That doesn’t mean you need to put up with someone who doesn’t do what you need. If you’re not getting enough of what you need, you can state that, and if it comes to it, you can leave. That’s OK. You’re still accepting that they are their own person who makes their own decisions. There can be upset, but there never needs to be bitterness.

Expectancy is things like “Can we …” and “I love it when …”. There’s no hint of judgment or suggestion that you think your partner is a worse person if they don’t want to do that thing. It recognises and respects their boundaries and autonomy. You’re always respected to state what you want, and they’re always respected to do the same—even if that doesn’t tally with yours.

With this dynamic, there’s no pressure to hide what you want. And it’s more likely you will get what you want, because nice people love doing nice things for other people when it’s appreciated and they don’t feel forced into it.