Questions & Answers about Bićemo prijatelji zauvek.
Bićemo means we will be.
It is the 1st person plural future tense of biti (to be):
- ja → biću = I will be
- ti → bićeš = you will be
- on/ona/ono → biće = he/she/it will be
- mi → bićemo = we will be
- vi → bićete = you will be
- oni/one/ona → biće = they will be
So in this sentence, bićemo already tells you the subject is we.
Because Serbian often drops subject pronouns when they are already clear from the verb ending.
Here, the ending -mo in bićemo already shows we, so mi is not necessary.
- Bićemo prijatelji zauvek. = We will be friends forever.
- Mi ćemo biti prijatelji zauvek. = also correct, but mi adds emphasis, like we in particular
Serbian does this much more often than English.