Which one is correct? or are they both correct?

[alejandrovig]

you can never know how your partner really is till you break up
you can never know what your partner is really like till you break up

[Rusty]

Both are correct, assuming you'll add proper punctuation and start the sentence with a capital letter.

The second sentence would be the more common thing to say.

[alejandrovig]

Thanks, Rusty)