1, 2, 3 are correct usages of 差一点儿，although I would probably say "他差一点儿爱上她，但她搞砸了“ for 2 and "他很早就起床了，但还是差一点儿没赶上火车" 4 is not correct, however… :(. What is written is actually "even though we all live in the same city, we almost saw each other." If you want to say what you wrote in English, you have to say, "我们虽然住在同一个城市，我们还是很少见到面。 " If you can say "almost" in English in the sense of "not quite, but close to occurring," then you can probably use 差一点儿。Also, the expression is almost always followed by a verb. (You don't use 差一点儿 in "There are almost 100 people here"). Other examples: 下雨后地面很滑，我差一点儿跌倒了。The ground was slippery after the rain, so I almost fell. 他突然从暗中出现，害我差一点心脏病发作。He suddenly appeared from the dark, and almost gave me a heart attack. 你这学期没好好用功，差一点考试不及格。You didn't study hard enough this semester, so you almost failed the exam. 他差一点就考进北京大学，好可惜没考上喔。He almost got into Beijing University, but too bad he didn't make it. 他开车不专心，差一点发生车祸。He wasn't paying attention while driving, so he almost got into an accident.

you understand information that phrase"差一点儿” contains ,but maybe you don't catch the feeling which delivered. sometimes or some occasions, we use other expression with same information instead of "差一点儿“, i don't think you should understand the reason by grammar,cause other expression also make sense on grammar,i think two different expressions deliver same information but different feeling that teller would like to express. example: 1.她跌倒了，差点儿受伤了。She fell down and almost hurt herself. 2.她跌倒了，没有受伤。She fell down but didn't hurt. the sentence 1 express strong feeling, but sentence 2 doesn't . Do you know what i mean ? you could contact me if you still have question.

即使咱们都住在同一座城市，我们差一点儿互相见面。 Even though we both live in the same city, we barely see each other. 正確 : 即使都住在同一座城市，我們也幾乎碰不上面。 咱們 就是 我們 不必在同一句裡 替換 也不必 重複使用 barely 在上例句裡 譯為中文時 應作否定用

「差一點兒」亦作「差一點」或「差點兒」。 您和其他網友的所有例句 只限定在 第一義 1 幾乎完成、實現某事。 如：「我們差一點兒就跑第一了。」 但是 還有第二義 2 程度、品質較為遜色。 如：「這個月的業績比上個月差一點兒。」 「她長得很漂亮，不過，就是脾氣差一點兒」。 「這個花瓶造型很漂亮，不過，就是畫工差一點兒」。 在第一義 差一點兒沒 = 差一點兒 差一點兒不 = 差一點兒 否定用法的意義與肯定用法相同時 是採取了 反諷修辭 我差點兒遲到了 = 我差點兒沒遲到 我差點兒死了 = 我差點兒沒死

you understand information that phrase"差一点儿” contains ,but maybe you don't catch the feeling which delivered. sometimes or some occasions, we use other expression with same information instead of "差一点儿“, i don't think you should understand the reason by grammar,cause other expression also make sense on grammar,i think two different expressions deliver same information but different feeling that people could have. example: 1.她跌倒了，差点儿受伤了。She fell down and almost hurt herself. 2.她跌倒了，没有受伤。She fell down but didn't hurt. the sentence 1 express strong feeling, but sentence 2 doesn't . Do you know what i mean ?