Yellow=What is incorrect

green= My corrections

Grey= My comments

I think that three months I have seen you last time, when "have passed since"you came to Brazil to learn our language.  "left Brazil after learning out language."     If he has already left then this sentence should be int he past-tense

I hope that your Portuguese be better "has improved".   

Your Brazilian friends they miss you. 

If you see me play a guitar now, you will be go crazy!!! I am much better now, I can play any music. And you? How better you are now? "Have you improved?" or "Have you gotten better at playing?"

I remember that you practiced every day when you were here.

Because you belived believed that Brazilian girls fall in love for with you if you can play romantic music, too bad you failed.  But life goes on, right? kkk.

My daily continue almost the same. This sentence is a little awkward these two sentences may sound better:"My days continue almost the same" or " My daily routine continues almost the same"

But, I am going to a the gym every Friday now, and I stopped drink soda, (comma not necessary)because I am taking care of my health.

Have you ever go a doctor do a checkup of your health?   "Have you ever gone to a doctor for a check-up?"

Take care this."Make sure to take care of your health"
Well, the main reason for me to be writing to you in English, It is because I decided to follow your advice and I started study studying English.

Now, I am studying English in Celin, but I am in still in the basic levels yet.

Do you have any advice to me learn faster? "Do you have any advice to help me learn faster?"

Your English is great! I hope to speak english as well as you.

When I will be become fluent, I will go visit you in your city. You must show me all the cool places in Boston. I hope you’re okay.

Writing an email to a friend.

How are you? How long has it been since we've seen each other? Three months, I think, when you came to Brazil to learn our language. I hope that your Portuguese has improved. Your Brazilian friends miss you! 

If you could see me play guitar now, you'd be way impressed! I am much better now and I can play just about any type of music. And you? How much better are you now? I remember that you practiced every day when you were here because you thought Brazilian girls would fall in love with you if you could play romantic music... too bad for you it didn't work out!  But life goes on, right?

Each day is about the same, but I am going to a gym every Friday and stopped drinking soda to take care of my health. Have you ever gone to a doctor for a checkup? Take care of yourself!

Well, the main reason I'm writing to you in English is because I've decided to follow your advice and start studying English. I study in Celin at the basic level. Do you have any advice to help me learn faster? Your English is so great! I hope to speak English as well as you someday. When I'm fluent, I will visit you in Boston. You must show me all the cool places. I hope you’re okay.

Att,

Lucas.

Writing an email to a friend.