Both are fine. In some contexts there is a slight difference between the meanings of sentences with the gerund and bare infinitive following verbs of perception. However, in this case, the meaning is the same. You're a mystery, aren't you, Pelin? Thousands of questions, but never an acknowledgement from you, never any thank yous....

Both are OK. using "crying" means you haven't seen them in the state of crying before, but they essentially mean the same thing. Hope this helped :)

I've never seen you cry before