Actually, I think the distinction between no longer being prepared and still being prepared is one of past (no longer) and present perfect tense (still). But it's a bit more complicated than that:
For example:
1. I was prepared to tell her on Sunday, but didn't get the chance. Here she comes now.
You may still be prepared to tell her, but it's no longer Sunday. Or in other words: you're not still prepared to tell her
on Sunday.
You can rephrase this as:
2. I had been prepared to tell her before I returned home on Sunday, but didn't get the chance. Here she comes now.
This is pretty similar to the above. The only difference is that in the second we have now two states/events: 1. "being prepared to tell her" and 2. "returning home". Event (2) ended state (1), so it's possible to put state (1) into the past perfect (past-in-the-past).
It's still possible to use the past tense here:
3. I was prepared to tell her before I returned home on Sunday, but didn't get the chance. Here she comes now.
The difference betwee version (2) and version (3) is that in version (2) you highlight the event of returning home, and then relate the state of being prepared to this point in time; you set both off from the present in the distant past - in a period that's over and done with. Thus you get the highlighted returning in the past tense, and the being prepared related to the returning (and coming before it) in the past perfect.
In version (2) you just view the two items as a temporal string: 1. I was prepared. 2. I returned home.
If you do not have a definite time in the past in mind, you can still use the past tense.
4. Yeah, I was prepared to tell her, but I never met her.
This suggests that the speaker has given up on telling her. The information could be irrelevant, she could have died, or the speaker could simply have changed his/her mind.
If you refer to the indefinite past, but you're still prepared to tell her, you'll have to use the present perfect tense:
5. Yeah, I've been prepared to tell her, but I've never met her.
Here we know that the speaker is still prepared to tell her, should he meet her.
Note that a sentence like (4) could easily refer to a specific point in time, too. You could be talking about a time when you know you both were in the same city. In this case, the same sentence does not imply anything about whether you're still prepared to tell her. It merely means that an opportunity is in the past. There is no information about what you would do if another opportunity arises. If you do not have spefic opportunity in mind, though, (4) does imply that you're no longer thinking of telling her.
Then, there's another set of affairs:
6. I'd been prepared to tell her, but then she was so mean to me. I've forgiven her since, and here she comes now.
See the tenses above? The sequence: 1. I'm prepared to tell her. 2. She's mean to me (and I no longer want to tell her.) 3. I forgive her (and I'm again prepared to tell her.) The moment of speaking co-incides with the "Here she comes now." In the past she was mean to me. I'm highlighting this as a crucial event, and I'm relating the "being prepared to tell her" to that.
Again, note that I don't have to highlight her being mean to me:
7. I was prepared to tell her, but then she was so mean to me, but I've forgiven her since, and here she comes now.
Instead of highlighting one event, you present both events as a sequence.
Similarly, you could think of the "I've forgiven" part as an event at a over-and-done-with time in the past:
8. I'd been (was) prepared to tell her, but then she was so mean to me, but I forgave her soon after that. Here she comes now.
Notice that you're ordering your events differently in (6/7) and in (8):
In (6) and (7) you're stating a past state of affairs: (being prepared --> her being mean). Then you're using that state of affairs a reference point for the presence ("I've forgiven her
since"). This is why you use present perfect in those examples.
In (8) you're stating a past state of affairs, too, but this time you're including the forgiving: (being prepared --> her being mean --> forgiving)
Tense
is very complicated, but the upside is that native speakers rarely get it wrong. However, problems can arise if a native speaker and a native listener apply different interpretations to the same sentences. As a writer, you'll need to balance verbal economy (as few words as possible) against clarity (the use of optional auxiliary verbs or "time phrases", that help a reader interpret the temporal relations that a text expresses). It
is very confusing. I'm not a native speaker, and took me a long time to properly understand the English tense system (tense in my mother tongue - German - is a lot simpler). I don't think I understood it properly until
after I graduated from University (where I studied English). I'm pretty sure I still make the occasional non-native speaker tense mistake.
I hope this isn't too confusing.