3. Mike and Alice are going steady (with one another).
You could just say, "Mike and Alice are dating."
Expressions 1 and 2 just state that the two are together as boyfriend and girlfriend.
Expression 3 is a little more subtle and means that Mike and Alice have been dating regularly and appear to have a stable relationship.
"Mike and Alice are dating."とシンプルに言えます。
1，2は二人が彼氏彼女の関係だという表現です。
3はちょっと微妙は表現で、マイクとアリスがデートを重ね、関係がしっかりしてきたときに使う言い方です。
"They have hooked up"- This is a very informal term/slang and can refer to dating or seeing someone casually.
Eg: "Kim and Jack hooked up last weekend"
Eg: "Kim and Jack hooked up years ago. They've been dating for forever"
"They are courting"- This is an older term but still refers to people dating and is still used.
Eg: "My mom always tells me how my dad and her were in love when they were courting"
I hope this helps :)
"“They have hooked up”は形式張らない用語またはスラングです。デート中であることや、誰かとカジュアルな恋愛のお試し期間中の関係であることを指します。例:”Kim and Jack hooked up last weekend”(キムとジャックは先週イチャついて過ごした)例:”Kim and Jack hooked up years ago. They’ve been dating forever.”(キムとジャックは何年も前に一緒になった。彼らは長期間デートしている。)
“They are courting”は”hook up”よりは古い用語ですが、これもデート中の人を表し、今でも使われています。例:”My mom tells me how my dad and her were in love when they were courting”(母は恋愛期間中も父と愛し合っていたことを私に話します)
ご参考にしていただければ幸いです。"
Couple (noun) - two people who are romantically associated
Seeing someone implies that you are romantically associated with another
_______________________________________
Examples
A: Is she single?
B: No, she is seeing someone
A: I would like to ask her on a date
B: She has a boyfriend
Couple (名詞)
- ロマンチックな関係にある二人
Seeing someoneは、他の人とロマンチックな関係にあることを意味しています
_______________________________________
例
A: Is she single?
（彼女はシングルかな？）
B: No, she is seeing someone
（いや、彼女には付き合っている人がいるよ）
A: I would like to ask her on a date
（彼女をデートに誘いたい）
B: She has a boyfriend
（彼女には彼氏がいるよ）
"Tom and Mary are in a relationship."
They are connected romantically.
"Tom and Mary are romantically involved."
This means that Tom and Mary have a relationship with each other in a romantic way.
"Tom and Mary are boyfriend and girlfriend."
Here you are describing the nature of their "friendship".
You could also say:
They are together.
"Tom and Mary are in a relationship."
ロマンスで結ばれている関係を表します。
"Tom and Mary are romantically involved."
トムとメアリーがロマンスで結ばれている関係を表します。
"Tom and Mary are boyfriend and girlfriend."
彼らの"friendship"という関係の性質について表現すればこうなります。
または以下のようにも言えます。
They are together.
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