请教英语高手，答案是对了，还是有些不明白，求翻译

Question

We missed you at this morning's meeting,Diana.
___B_,but if I hadn't had to meet a friend,I would have been there.
AMe,too.B I'm sorry.C Never mind .D Thank you .
would have done,could have done,should have done 有什么区别呢？

Answer 1

would have done-----表示过去将要做什么
could have done-----表示过去有能力做什么
should have done-----表示本应该做的事情，实际上没做成追问

_,but if I hadn't had to meet a friend,I would have been there请求翻译，这语法怎么解释

追答

中文意思是，如果 我 不是 不得不 见一个朋友，我当时就能去了，（能去参加会议）