hitori de nagai kaigi ni deruno ha tumaranai node, douryou mo issyo da to tasukaru.

一人で means alone or by oneself.

In this sentence, で shows the manner or condition in which the action happens. So:

• 一人 = one person / alone
• 一人で = alone, by oneself

It does not mean a location here. It tells you how the speaker would attend the meeting.

The verb 出る can mean to attend when used with events such as:

• 会議に出る = attend a meeting
• 授業に出る = attend class
• 試合に出る = participate in a match

With this usage, the event is marked by に, not を.

By contrast, 部屋を出る means leave a room, where を marks the place you move out of. So the particle changes depending on the meaning of 出る.

The の turns the verb phrase into a noun-like phrase.

• 会議に出る = to attend a meeting
• 会議に出るの = attending a meeting

Then は marks that whole idea as the topic:

• 一人で長い会議に出るのはつまらない
• As for attending a long meeting alone, it is boring

This is a very common pattern in Japanese:

• V-るのは... = the act of V-ing is...
• V-ることは... can also be used, though の often feels more direct and conversational here

長い会議 simply means a long meeting.

Japanese often uses adjectives directly before nouns just like English:

• 長い会議 = long meeting
• 短い会議 = short meeting
• 楽しい会議 = enjoyable meeting

There is nothing especially unusual here; it is just describing the meeting.

Both ので and から can mean because, but they have slightly different tones.

• ので sounds a bit softer, more explanatory, and less blunt
• から can sound more direct or more strongly personal

So:

• つまらないので = because it is boring
• つまらないから = because it is boring

In this sentence, ので fits well because the speaker is giving a reason in a mild, natural way.

同僚 means colleague or coworker.
The particle も usually means also, too, or as well.

Here, 同僚も suggests something like:

• if a colleague comes too
• if my colleague is there as well

The nuance is that the speaker does not want to be the only one there. Having a colleague there too would make things better.

Depending on context, English might not always translate the も very literally, but the idea of also / too is still there.

一緒 means together or the same company.

• 同僚も一緒だ = a colleague is together with me / comes along too
• 同僚も一緒だと = if a colleague comes too / if a colleague is with me

The と here is a conditional particle meaning if/when.

So 同僚も一緒だと助かる means something like:

• It would help if a colleague came too
• I’d appreciate it if a colleague were with me

That is because 一緒 is being used differently here.

1. 一緒に as an adverb

This means together and modifies a verb:

• 同僚と一緒に行く = go together with a colleague

2. 一緒だ as a predicate

This means to be together / to be with someone:

• 同僚も一緒だ = a colleague is with me too

In your sentence, the pattern is:

• 同僚も一緒だと助かる
• If a colleague is with me too, that would help

So だ is needed because 一緒 is acting like the main predicate before the conditional と.

Literally, 助かる can mean to be saved or to be helped, but in everyday Japanese it very often means:

• that would help
• I’d appreciate that
• that would make things easier

So here, 同僚も一緒だと助かる does not sound dramatic. It simply means that having a colleague there would be convenient or reassuring.

This is a very common nuance in Japanese.

Examples:

• 早く返事をもらえると助かります。 = It would help if I could get a reply soon.
• 手伝ってくれると助かる。 = I’d appreciate it if you helped.

Japanese often leaves the subject unstated when it is clear from context.

In this sentence, the implied subject is most naturally I or for me:

• Attending a long meeting alone is boring, so it would help if a colleague came too.

Japanese does this all the time. Instead of repeating pronouns like I, you, or they, the language often lets context do the work.

つまらない usually means:

• boring
• dull
• uninteresting

But depending on context, it can also suggest:

• not enjoyable
• not satisfying
• kind of depressing / no fun

In this sentence, it is not just saying the meeting itself is boring in an objective way. It also suggests that attending it alone is unpleasant or no fun.

So the feeling is close to:

• It’s boring / no fun to attend a long meeting alone.

Yes. A very literal translation is helpful for grammar, but a natural English version might be:

• Attending a long meeting alone is boring, so I’d appreciate it if a colleague came too.
• Going to a long meeting by myself is no fun, so it would help if a coworker came along too.
• Since long meetings are boring when I’m alone, it’d be nice if a colleague were there too.

All of these capture the same basic meaning, even though they are not word-for-word translations.