Hello my dear friend Hemal, . ¶
I hope that everything is okay with you. or I hope you are well.

Last Saturday, I went to Joan's birthday party, andwhere I wore a red dress.

Another option would be to use two sentences.

I wanted to look wonderbeautiful for him, because, as you know, I'm in love with him.

It's not clear here who "he" is, so we have to assume that your friend Hemal already knows who you are talking about.

When I arrived at the party, I could see a lot of food and especially, but I mostly just saw him.

It's a bit odd here that you would compare the man you are in love with with food, so I would reword the sentence.

He looked amazing, but he was with another girl, so I felt sad.

But it's okay because I still ate delicious food.

I send you many kisses, and I hope to see you soon.

This is fine, but it would sound better to say "I'm sending you lots of kisses"

Your beautiful friend, Camila.

It sounds a bit odd to call yourself beautiful

(Hello m) / (My dear friend Hemal), ¶
I hope that everything is okay.

You've combined a neutral greeting with a very formal one. Depending on the tone you're looking for, you should pick one, but not both.

I wanted to look wonderful for him, as, as you know, I'm in love with him.

In a more casual style you could omit the as here, but the rest of this email is written in a formal style, so it's better to avoid the omissions

I'm sending you many kisses, and I hope to see you soon.

Your beautiful friend, Camila.

Beautiful is generally not an adjective you would apply to yourself. That's the kind of adjective you only use for other people, as applying it to yourself sounds arrogant.