Estas são minhas sugestões de correções. Só sugestões. Parabéns pelo seu texto.
How have you been? We last saw each other at our high school graduation, right? What have you done since then?
Well, as soon as I graduated from high school, I got into College to study Computer Science but I dropped out of it in the first year because I didn't like the course at all; I have to say that it was my fault, because I only applied for this course considering it as a highly paying career. I hadn’t given much thought to it before, if this was what I really wanted to do. I was seventeen at the time, I was very immature and I was easily led by others opinion.
Do you remember Jennifer, the girl who I have fallen in love with? Well, I took courage and I opened my heart to her. To make things short, we started dating and we got married in 2010. We’ve been married for four years now and we have one kid and another one is just coming around the corner.
Have you heard about Bruno? The boy who used to be a real troublemaker? He is a doctor now. He is currently living in Africa, working in a NGO who takes care of poor children, who would say?
That is all my friend, I hope to hear from you soon.
We say dropped out of university…. (larguei a universidade)
Computer Science : Ciência da computação
Summarising, significa resumir, mas neste sentido de uma carta informal para um amigo, você precisa de um link mais informal, por isso o uso de to make things short (para resumir...)
Quando finalizamos uma carta para um amigo em inglês, usamos I hope to hear from you soon .