Learn Hardcore Japanese: watasi ha kare to tukiatte imasu.

To accompany someone / go along with someone
- 友だちに頼まれて、買い物に付き合った。
  → My friend asked me, so I went shopping with them.
To socialize / hang out with someone
- 彼とは長い間付き合っている。
  → I’ve been associating with him for a long time (we’ve known each other for a long time).
To be in a romantic relationship / to date
- 私は彼と付き合っています。
  → I’m dating him / I’m in a relationship with him.

In the sentence you gave, context makes it clear we’re using meaning (3): “to go out with / to date (someone).”

Why is it 彼と and not 彼を? What does the particle と do here?

The particle と often means “with” when talking about:

mutual actions
reciprocal relationships
partners in some shared activity

付き合う describes a mutual relationship, not a one-way action. Both people are involved equally in the relationship, so Japanese marks the partner with と:

私は彼と付き合っています。
→ I am in a (mutual) relationship with him.

Using を would sound wrong here, because を marks a direct object of a one-way action (like 食べる, 読む, 見る). Dating is not something you do to him; it’s something you do with him.

So:
付き合う + と = to be in a relationship with X / to associate with X.

What exactly is the role of は in 私は here? Is it the subject?

は is a topic marker, not a grammatical subject marker.

In 私は彼と付き合っています, 私 is being presented as the topic:

私は → As for me / Speaking about me…
彼と付き合っています → I’m dating him.

In English we often treat the topic as the subject in translation, but in Japanese:

は = “this is what I’m talking about now”
が = marks a grammatical subject more explicitly (especially when introducing new information or contrasting).

Here, 私は is very natural because you’re just talking about yourself as the topic. In conversation, Japanese people would very often omit 私は entirely if it is clear from context who is talking.

Does 付き合っています mean “I am dating him right now (this moment)” or “I’m in a relationship with him (in general)”?

付き合っています here expresses a current state, not a temporary action happening at this instant.

The pattern is:

ている (て + いる) can express:
1. Ongoing action – something happening right now
  - 本を読んでいます。→ I am reading a book (right now).
2. Resulting state / current condition – something that has happened and its result continues
  - 結婚しています。→ I am married (I’m in the state of being married).

付き合う is like “to start going out / to get together.”
付き合っている describes the state that results: being in an ongoing relationship.

So 私は彼と付き合っています means:

I am (currently) in a relationship with him
He is (currently) my boyfriend / partner

Not “I am in the middle of going on a date with him right now.”

What is the difference between 付き合っています and 付き合っている?

The difference is mainly politeness level, not meaning.

付き合っています
- Polite form (〜ます style)
- Used in normal polite conversation, with people you’re not close to, at work, etc.
付き合っている
- Plain form (dictionary style)
- Used with friends, family, people close to you, in casual writing, diaries, etc.

In very casual speech, 付き合っている often gets shortened to:

付き合ってる (つきあってる)

All three:

付き合っています
付き合っている
付き合ってる

have the same basic meaning: is/are dating; is/are going out.
You just choose the form that matches the level of formality you need.

Is 私 necessary here? Would people actually say 私は彼と付き合っています in conversation?

In natural conversation, 私 is often dropped when it’s obvious who the speaker is.

So these are all possible:

私は彼と付き合っています。
→ Clear, polite, slightly more explicit.
彼と付き合っています。
→ Very natural in real speech when context already makes “I” obvious.

In many situations, the shorter 彼と付き合っています is more typical.

About 私 itself:

私 (わたし) is:
- Gender-neutral in formal situations
- Common for women in most contexts
- Common for men in formal / polite contexts, but many men switch to 僕 (ぼく) or 俺 (おれ) in casual situations.

So a man might say casually to a friend:

俺、彼と付き合ってる。
僕、彼と付き合ってる。

A woman might say:

私、彼と付き合ってる。

But again, often the pronoun is simply omitted.

Can a man say this sentence? Does 彼 automatically mean “boyfriend,” or just “he”?

Grammatically, anyone (man or woman, non-binary, etc.) can say:

私は彼と付き合っています。

What 彼 means depends on context:

On its own, 彼 = he / that guy / that man.
But in combination with 付き合っています, it almost always implies:
- He is my boyfriend / male romantic partner.

So:

If a woman says it, it’s usually understood as:
- I am dating him (he’s my boyfriend).
If a man says it, it normally suggests:
- I am dating him (he’s my boyfriend → a same-sex relationship).

Contemporary Japanese does allow that; it’s not grammatically special—just a matter of social/cultural context.

If you want to make “boyfriend” especially clear, you might also hear:

彼は私の彼氏です。
→ He is my boyfriend.

How do I say “I’m not dating him” in Japanese using this pattern?

You just negate the 〜ています part.

Polite negative:

私は彼と付き合っていません。
→ I’m not dating him. / I’m not in a relationship with him.

Casual negative:

私は彼と付き合っていない。
Or even more casual: 彼と付き合ってない。

All mean roughly the same; the main difference is politeness level.

Does 付き合う only mean “to date,” or are there other common meanings I should know?

付き合う has several common meanings, depending on context:

To date / be in a romantic relationship
- 彼と付き合っている。
  → I’m dating him.
To accompany someone / go along with someone (not necessarily romantic)
- 友だちに付き合って、映画を見に行った。
  → I went to the movies with my friend (to keep them company).
To socialize / associate with someone
- 彼とは仕事だけの付き合いだ。
  → I only associate with him for work (we’re just work acquaintances).
To go along with someone’s plan / put up with something for someone’s sake
- 夜遅くまで彼の飲みに付き合った。
  → I stayed out late drinking with him (for his sake / to keep him company).

So you always need to read 付き合う in context.
In your sentence with 彼と付き合っています, it’s clearly romantic.

What’s the difference between 彼 and 彼氏 (かれし)? Could I say 私は彼氏と付き合っています?

彼 (かれ)
- Basic meaning: he / him / that guy
- In contexts like 彼と付き合っています, it’s naturally understood as “my boyfriend,” but that’s from context, not the word itself.
彼氏 (かれし)
- Means boyfriend specifically
- It’s a noun for the role (boyfriend), not a pronoun like “he.”

So:

私は彼と付き合っています。
→ I’m dating him (he’s my boyfriend).
私には彼氏がいます。
→ I have a boyfriend.

私は彼氏と付き合っています is grammatically okay but sounds a bit redundant (like saying “I’m going out with my boyfriend” when “boyfriend” already implies that). Native speakers usually say one or the other, not both together like that, unless they’re emphasizing something unusual.

Can I change the word order, like 彼と私は付き合っています? Does that sound natural?

You can say 彼と私は付き合っています, and it’s grammatically correct, but the nuance shifts slightly.

私は彼と付き合っています。
- Normal, neutral way to say I’m dating him.
- Topic: 私 (me).
彼と私は付き合っています。
- Emphasis feels more like “He and I are dating (each other).”
- Both 彼 and 私 are grouped together as a pair.
- It can be used if you want to stress the pair, for example when clarifying relationships.

Even more natural in many conversations is simply:

彼と付き合っています。
(dropping 私)

because the listener already knows you’re talking about yourself.

How would I say how long I’ve been dating him, using this same pattern?

You can add a time expression before 付き合っています:

私は彼と３年付き合っています。
→ I’ve been dating him for three years.

Common patterns:

〜から付き合っています (since ~)
- 彼と高校のときから付き合っています。
  → I’ve been dating him since high school.
〜前から付き合っています (since ~ ago)
- 彼と１年前から付き合っています。
  → I’ve been dating him since a year ago.

The 〜ています form works well with time expressions to mean “have been doing (and still am)”.

Is 付き合う written in kanji or kana? I see both 付き合う and つき合う or 付きあう sometimes.

You’ll see various writings, all read つきあう:

付き合う
つき合う
付きあう
つきあう

All are acceptable; in modern writing, 付き合う (mixed kanji + kana) or つきあう (all kana) are very common.

In your sentence:

私は彼と付き合っています。

using 付き合う is perfectly standard. Some writers prefer more kana (つきあう) for a softer or easier-to-read style, but there’s no change in meaning.