ما منتظر دوستمان هستیم، چون با او قرار داریم.

دوستمان means our friend.

It is built like this:

• دوست = friend
• -مان = our

So دوستمان is friend + our.

It is singular: our friend.
If you wanted our friends, you would usually say دوستانمان or دوست‌هایمان.

Because Persian does not say wait for the same way English does.

In this sentence, منتظر means waiting / expectant, and the person being waited for comes after it directly. So Persian expresses this idea more like:

• we are waiting our friend
• or more literally, we are in a waiting state for our friend

You do not add a separate word equivalent to English for here.

Yes. There is an ezafe sound, pronounced like a short -e.

So although it is written:

• منتظر دوستمان

it is pronounced:

• منتظرِ دوستمان
• montazer-e doostemân

This ezafe links منتظر to the following noun. In normal Persian writing, short vowels are often not written, so learners have to supply them from grammar and experience.

In Persian, منتظر is not a finite verb here. It is an adjective-like predicate meaning waiting or expectant, so Persian uses بودن (to be) with it:

• منتظر هستیم = we are waiting

So the structure is literally closer to:

• we are waiting / we are in a waiting state

This is a very normal Persian pattern: a state word + بودن.

Here, قرار داریم means something like:

• we have an appointment
• we have plans
• we have arranged to meet

The word قرار can mean an arrangement, appointment, or meeting plan. With با + a person, it often means that a meeting has been arranged with that person.

So:

• با او قرار داریم = we have an appointment / arrangement with him or her

It can, depending on context, but it does not have to.

قرار with a person can mean:

• an appointment
• a planned meeting
• a date

So با او قرار داریم could be romantic in the right context, but by itself it simply means there is an arranged meeting. You need context to know whether it is romantic or not.

Because با means with, and after a preposition like با, Persian uses the pronoun directly:

• با او = with him / with her

The marker را is used for a direct object, not after prepositions.

So:

• او را = him/her as a direct object
• با او = with him/her

In everyday spoken Persian, با او is often said as باهاش.

It can mean either him or her.

Persian third-person singular pronouns do not mark gender the way English does. So او is gender-neutral in this sentence. The listener figures it out from context.

Because Persian usually places the main verb or copula near the end of the clause.

In this sentence:

• ما منتظر دوستمان هستیم
• چون با او قرار داریم

both clauses end with the verbal element:

• هستیم
• داریم

This is very normal for Persian. English speakers often notice this quickly because English usually puts the verb earlier.

Yes. Persian often drops subject pronouns when the verb already makes the person clear.

Since هستیم and داریم both show we, you can say:

• منتظر دوستمان هستیم، چون با او قرار داریم.

This is still completely clear.
Including ما adds emphasis, contrast, or just a bit more explicitness.

A natural spoken version would often be:

• منتظرِ دوستمون هستیم، چون باهاش قرار داریم.

Main spoken changes:

• دوستمان → دوستمون
• با او → باهاش

You may also hear the subject dropped:

• منتظرِ دوستمون هستیم، چون باهاش قرار داریم.

The original sentence is standard and correct, but the spoken version sounds more everyday and conversational.