you
I'm telling you you should leave now.
The sentence informally tells someone they should leave now — 'you' as direct object of 'telling', then 'you' as subject of the embedded clause 'you should leave', with the conjunction 'that' omitted.
Meanings (pronounced /juː/)
the person or persons being addressed, used as the object of a verb or preposition
- I'll call you tomorrow.
- This is for you.
the person or persons being addressed, used as the subject of a verb
- You are next in line.
- Did you see the news?
Word origin
From Old English ēow, the dative/accusative plural form of 'thou'. Originally 'you' was strictly plural (with 'thou' as singular), but starting in the 13th century 'you' came to be used as a polite singular as well, eventually displacing 'thou' entirely except in archaic religious texts. The merger of 'thou' and 'you' is one of the most consequential changes in English pronoun history.
Fun fact
Until about 1700, English distinguished singular 'thou' from plural 'you'. Quakers famously kept using 'thou' for centuries as an egalitarian gesture — 'thou' was the form one used with intimates and inferiors, so addressing everyone with 'thou' meant treating everyone as equally close. The triumph of 'you' for both singular and plural is the reason American English now sometimes invents 'y'all', 'you guys', or 'youse' to recover a plural marker.