Olá Gabriela. Sugestões e correções para seu e-mail:
I heard you got fired from your job, and that you are very sad, so I am writing you this email. I know losing a job is hard but you can't be sad and depressed.
Dear friend, don't worry. (I'm sure) everything will work out (for the best). I think you were working a lot and you didn't have much time to go out with your friends and relax.
It's necessary that you stay positive / think positively. Besides, now is a good opportunity for you to improve your qualifications and take new courses before you find a new job.
I've had an idea. Would you like me to go and visit you? I can help you through this. We could go to our favorite band's concert, go out with (our) friends, go for a walk along the beach or simply talk.
1) Termos entre parênteses são sugestões opcionais, e termos separados pela barra (/) são intercambiáveis entre si.
2) Lembre-se de diferenciar o apóstrofo ( ' ) do acento agudo ( ´ ). O inglês usa o apóstrofo.
Você tem um bom domínio do idioma. Keep it up!