Meaning of sentences using "didn’t", "wasn't" and "wouldn't"

Question

What are the meanings of the sentences below?
What exactly is the difference in meaning?
Do sentences using wasn't and wouldn't have the same meaning?

a) "...but he didn't leave."
b) "...but he wasn't leaving."
c) "...but wouldn't leave."

Answer 1

Sentence (a):

But he didn't leave.

makes a statement about something that happened in the past, as if a person were recalling it afterward. Imagine a situation where a person had been sitting in a bar, drinking a glass of beer. Then (for example),

He pushed the empty glass away and looked around. But he didn't leave.

Sentence (b):

But he wasn't leaving.

expresses action in the continuing past, rather than in the simple past. For example,

He was slowly counting the money from his pocket, after looking groggily at the clock above the bartender's head. But he wasn't leaving.

Sentence (c):

But he wouldn't leave.

describes a conditional situation. In this case, wouldn't, the negative form of the conditional verb would, focuses on a person's unwillingness to do something. Idiomatically, "would not" means "refused to." Thus, for example:

The bartender told him that it was time for the bar to close and for him to go home. But he wouldn't leave.

Answer 2

Let’s examine each example one at the time:

a) …he didn’t leave

It is simple past, that is an action started and completed somewhere in the past; as we can see that’s the way the negation is made.

b) …he wasn’t leaving

It is simple past too, it can express a same kind of action as previously shown but can also express the idea of some continuity in the past, between some unspecified time sequences, or an interruption or not of the action by another action:

he was leaving when I came, or he was not leaving when I came.

c) …he wouldn’t leave

It can express the future (the negative form):

he said he wouldn’t leave

or it can express the conditional (the negative form):

If I went there he wouldn’t leave

Answer 3

a) If he truly "didn't leave", that means he's still there. However, if you specify that he didn't leave AT SOME PARTICULAR TIME, then he might have left later.

b) At that particular time in the past he was not in the process of leaving. We do not know whether he left after that.

c) He refused to leave. (We asked him to, but he would not.)