Ich muss jetzt leider los, weil ich einen Termin im Büro habe.

In Ich muss los, los is part of a very common idiomatic expression meaning I have to go or I have to leave.

By itself, los often has the idea of off, away, or getting started. So Ich muss los is like saying I have to get going.

It is not translated word for word into natural English. You should learn müssen + los here as a set phrase.

Because Ich muss los is already a complete and natural expression in German.

English usually needs a verb like go or leave, but German can express the idea with muss los. It sounds very normal in speech, especially when someone is about to leave.

You can also say Ich muss gehen, but that is a bit more literal. Ich muss los is often more idiomatic and conversational.

Yes, slightly.

• Ich muss los = I have to go / I have to get going

  • very common in everyday conversation
  • often used when ending a visit, call, or meeting

• Ich muss gehen = I have to go

  • also correct
  • a bit more neutral or literal

So in this sentence, Ich muss jetzt leider los sounds very natural for politely leaving.

Because German main clauses usually follow the verb-second rule.

In Ich muss jetzt leider los:

• Ich = first element
• muss = finite verb, so it goes second
• jetzt leider los = the rest of the clause

This is one of the most important word-order rules in German.

Because weil introduces a subordinate clause, and in German subordinate clauses the finite verb usually goes to the end.

So:

• main clause: Ich muss jetzt leider los
• subordinate clause: weil ich einen Termin im Büro habe

That is why habe comes last.

Compare:

• Ich habe einen Termin.
• ..., weil ich einen Termin habe.

In German, subordinate clauses are normally separated from the main clause by a comma.

Since weil introduces a subordinate clause, the comma is required:

• Ich muss jetzt leider los, weil ich einen Termin im Büro habe.

This is standard German punctuation.

Because Termin is a masculine noun, and here it is the direct object of habe.

The base form is:

• der Termin

In the accusative singular, der-words and related forms change:

• ein Termin = nominative
• einen Termin = accusative

Since the sentence means I have an appointment, Termin is the thing being had, so it is in the accusative:

• ich habe einen Termin

Termin usually means appointment, scheduled meeting, or arranged time.

In this sentence, einen Termin haben means to have an appointment.

A useful warning: Termin is not the same as the English word term in most situations. It usually refers to something scheduled in a calendar.

Examples:

• Ich habe morgen einen Termin beim Arzt. = I have a doctor’s appointment tomorrow.
• Wir haben um drei einen Termin. = We have an appointment at three.

Im is a contraction of in dem:

• in dem Büro → im Büro

German uses this contraction very often.

Also, im Büro is in the dative here because it describes a location, not movement:

• im Büro = in the office / at the office

Compare:

• Ich bin im Büro. = I am in the office.
• Ich gehe ins Büro. = I am going into the office.

So in your sentence, the meaning is location: the appointment is at/in the office.

Leider means unfortunately.

It shows that the speaker regrets having to leave. Without leider, the sentence would sound more neutral:

• Ich muss jetzt los = I have to go now
• Ich muss jetzt leider los = Unfortunately, I have to go now

So leider adds politeness and a sense of regret.

Yes, the word order can change, but the version in the sentence sounds very natural.

• Ich muss jetzt leider los
• Ich muss leider jetzt los

Both are possible, but the first one is often more natural in everyday speech.

Very roughly:

• jetzt gives the time
• leider comments on the whole situation

German adverb order is somewhat flexible, but not random. The sentence you have is a common and idiomatic order.

No, not in normal standard German.

You need a subject in the weil clause:

• ..., weil ich einen Termin im Büro habe

German does not usually omit the subject the way some languages do. Even though the subject is the same person as in the first clause, you still repeat ich.

Yes, but the structure changes.

With denn, the word order stays like a main clause:

• Ich muss jetzt leider los, denn ich habe einen Termin im Büro.

With weil, the verb goes to the end:

• Ich muss jetzt leider los, weil ich einen Termin im Büro habe.

Both can mean because, but weil is especially common in everyday German.