tomodati ha atarasii eiga wo mitagatte ita node, konya issyo ni eigakan he iku.

見たい is normally used for your own desire: I want to see it.

When you talk about someone else’s apparent desire, Japanese often uses 〜たがる instead. So:

• 見たい = want to see
• 見たがる = show signs of wanting to see

Since 友達 is another person, 見たがっていた is the natural form. It means something like:

• was wanting to see it
• seemed to want to see it

This is a very common point for English speakers, because English does not usually make this distinction.

〜たがる is attached to the ます-stem of a verb and expresses that someone appears to want to do something.

Examples:

• 行きたがる = seem to want to go
• 食べたがる = seem to want to eat
• 見たがる = seem to want to watch/see

So:

• 見る → 見たがる
• 見たがっていた = was showing a desire to watch

It often has the nuance that you know this from their behavior, words, or situation, not from directly feeling it yourself.

見たがっていた uses 〜ている, which here describes an ongoing state or condition in the past.

So:

• 見たがった = wanted to see it / showed that desire at some point
• 見たがっていた = was wanting to see it / had been wanting to see it

In this sentence, 見たがっていた sounds natural because it sets up the reason for going tonight: the friend had been wanting to watch the new movie.

ので means because or since. It gives a reason.

In this sentence:

• 友達は新しい映画を見たがっていたので = because my friend wanted to see the new movie

Then the result follows:

• 今夜一緒に映画館へ行く = (we/I) will go to the movie theater together tonight

Compared with から, ので often sounds a little softer, more explanatory, and a bit less direct.

Both can mean because, but the tone is a little different.

• から can sound more direct, personal, or assertive.
• ので often sounds more neutral, polite, or explanatory.

So these are both possible in many situations:

• 友達は新しい映画を見たがっていたから、今夜一緒に映画館へ行く。
• 友達は新しい映画を見たがっていたので、今夜一緒に映画館へ行く。

The version with ので sounds a little smoother and more matter-of-fact.

は marks 友達 as the topic of the first part of the sentence.

• 友達は新しい映画を見たがっていた = As for my friend, they wanted to see the new movie

This does not necessarily mean strong contrast, though は can sometimes suggest it. Here it is probably just setting up the friend as the topic being discussed.

A learner might expect が, and that could also be possible in some contexts. Very roughly:

• 友達は = speaking about the friend as the topic
• 友達が = emphasizing that it was the friend who wanted to see it

In many everyday sentences, both may be possible depending on nuance.

を marks the direct object of the verb.

Here, the verb is based on 見る = to see/watch. The thing being watched is 新しい映画.

So:

• 新しい映画を見たがっていた = wanted to watch the new movie

That is why 映画 takes を.

In Japanese, the plain non-past form often covers both:

• present
• future

So 行く can mean:

• go
• will go
• am going to go

Because the time word 今夜 already tells you this is in the future, 行く is understood as future here.

This is very normal in Japanese.

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

So 今夜一緒に映画館へ行く could mean:

• I’m going to the movie theater together with my friend tonight
• We’re going to the movie theater together tonight

In English, you usually must choose a subject. In Japanese, it can stay omitted.

Since the sentence says 一緒に and the earlier topic is 友達, the listener will understand that the speaker and the friend are going together.

一緒 means together. The particle に turns it into an adverbial expression:

• 一緒に = together

So:

• 今夜一緒に映画館へ行く = go to the movie theater together tonight

This is just the normal form of the expression. English speakers often try to analyze に very literally, but it is best to learn 一緒に as a fixed, common phrase.

Both へ and に can mark direction with verbs like 行く.

• 映画館へ行く
• 映画館に行く

Both mean go to the movie theater.

The difference is small:

• へ emphasizes direction somewhat more
• に can feel a bit more like arrival at a destination

In modern Japanese, both are common, and in many cases either one would work.

Yes, in natural English this would usually be translated as my friend or a friend, depending on context.

Japanese often leaves out things like:

• my
• your
• the
• plural markers

So 友達 by itself can mean:

• friend
• a friend
• my friend
• friends

Context decides.

In this sentence, my friend is the most natural interpretation.

Japanese modifiers come before the noun they describe.

So:

• 新しい映画 = new movie

This is the standard order in Japanese:

• 大きい家 = big house
• 面白い本 = interesting book
• 新しい映画 = new movie

Unlike English, you do not need a or the in Japanese.

Yes, it is understandable and basically natural.

A very natural English interpretation is:

• Because my friend wanted to see the new movie, we’re going to the movie theater together tonight.

Depending on context, a Japanese speaker might also say things a little differently, such as using 友達が instead of 友達は, but the original sentence is grammatically fine and easy to understand.

This combination is normal.

The first part gives the reason, and that reason happened earlier or was already true:

• 友達は新しい映画を見たがっていた = my friend had been wanting to see the new movie

The second part tells what will happen as a result:

• 今夜一緒に映画館へ行く = so we’re going to the movie theater tonight

So the timeline is:

1. the friend wanted to see the movie
2. because of that, tonight they will go

That tense combination is very common in Japanese.