Can I say "Lubię ciebie"?
Not really, unless you want to emphasize 'ciebie' (e.g. "Lubię ciebie a nie jego" - "I like YOU and not HIM").
Most of the time you'd say "Lubię cię".
Why not "Lubię cię." ?
It's one of the starred answers.
It said another accepted phrase was 'Lubię was' .... was was not even in the selection of words to choose from.
When do I use "cebie" and when "was"?
"ciebie" is an empasized variant of "cię", so it would rather work in a sentence like "I like YOU, not him!".
"Lubię cię" = I like you, Sven.
"Lubię was" = I like you, Sven and Matilda.