You must have formed some opinion of me .你对我一定是有看法的。

Must have done sth.对过去发生的事所做的判断或猜测，通常只在对说的内容的准确性把握比较大时使用。

例：
It must have cost him a lot to buy the eatate.
他买下那套房子一定花了不少钱。