I was sleeping/I slept

Probably a question of frequency: 'slept' once; 'was sleeping' somewhat regularly. Some might prefer the past perfect 'had slept' over the simple past.

Can "slept" in this case mean that I slept with her various times?

It can, but my first assumption was that it was once.

I don't really understand why. When we say: I was crying yesterday. it simply means that we were crying.

whatchadoinI don't really understand why.

No adverbs to disambiguate. Most native speakers will take the first of these below (and only the first) to mean "one time" because there's nothing else in the sentence that says otherwise.

I slept with her.
I slept with her often.
I slept with her every night.
I slept with

CalifJimOf course. That's a tautology. If you say, "Yes", it means yes. If you say, "No", it means no.

So, when I say "I was crying yesterday." it can't mean that I was crying a couple of times during that day?

whatchadoinSo, when I say "I was crying yesterday." it can't mean that I was crying a couple of times during that day?

It's very unlikely that anyone would think that that's what you meant.

CJ