Question

1. Until I missed him very much, I called him.

2. Until I missed him very much, I had called him.

(Which one is grammatical?)

3. That I missed her very much was real.
4. It was real that I missed her so much.
(Are both grammatical?)

5. I was so tired, so I stayed in bed until 10 a.m.

(Does this sentence mean that he slept until 10 a.m.?)

Answer 1

#1 is best. Both clauses use the past tense. #2, no, because you change tenses from past to past perfect.

#3 & #4. I don't really like either of them, but they are grammatical. #4 would be better if "so" was replaced by "very". #3 is very informal and might be okay in a sentence, but "that" is a pronoun with no antecedent here. In #4 it is a conjunction which is used correctly.

"That" has at least three uses:

https://www.bing.com/search?q=that+-+definition&form=EDGNTC&qs=PF&cvid=400eefe58b3f4d1d8e02e075c2a0fe13&pq=that%20-%20definition

#5 is fine. It does not say he slept until 10:00, though. He could have been staring at the ceiling, reading, watching television, or sleeping.