I have a boyfriend.We have been together for three years,and I love him very much.
（you need to use a period)
其他的.
We have been together for three years and I love him very much.(This sentence doesn't need a comma.)
In high school,whenever I feel depressed for grades sad (for grades sad?What is this?)
應(yīng)該是：
In high school whenever I feel depressed about bad grades,he is always very considerate.He comforts and encourages me.（這樣比較好）
這樣比較好：
I have a boyfriend.We have been together for three years and I love him very much.
In high school whenever I feel depressed about bad grades he is always very considerate.
He comforts and encourages me.We have experienced a lot in three years.
Perhaps some people don't think we will make it,but we have come over many problems
and hope to keep going.