语法上有错,它不是个句子,because连接的原因从句中缺少主语,并且没有主句.举两个例子你就明白了：
He was writting to you because he missed you.（因为他想你,所以他给你写信.）
I am here because I miss you.（因为我想你,所以我来这里了.）
because of 也是“因为”的意思,不过应该是because of sth/doing sth.譬如：He was writting to you because of missing you so much.