shuumatsu ni tomodachi to issho ni hanabi o mi ni iku node, ima kara wakuwakushite imasu.

I’m already excited because I’m going to go see fireworks with a friend on the weekend.

Breakdown of shuumatsu ni tomodachi to issho ni hanabi o mi ni iku node, ima kara wakuwakushite imasu.

• を: direct object particle
• 友とも達だち: friend
• と: companion particle
• に: time particle

Questions & Answers about shuumatsu ni tomodachi to issho ni hanabi o mi ni iku node, ima kara wakuwakushite imasu.

Why are there so many に particles in this sentence? Are they all doing the same thing?

No, each に is doing a different job here.

• 週末に = at/on the weekend
  This に marks a time.

• 一緒に = together
  Here, に turns 一緒 into an adverb-like expression, so it describes how you go.

• 見に行く = go to see
  This に is used in the pattern verb stem + に + 行く / 来る, which shows purpose.

So although they all look the same, their functions are different:

• time marker
• adverbial marker
• purpose marker

What does 友達と一緒に mean? Why do we need both と and 一緒に?

友達と一緒に means together with a friend / with friends.

• 友達と = with a friend / with friends
• 一緒に = together

Using both makes the idea more explicit: not just with a friend, but going together with a friend.

Compare:

• 友達と行く = go with a friend
• 友達と一緒に行く = go together with a friend

Very often, 一緒に adds a feeling of doing something side by side.