What does Si y no tu eres simpatica mean?

Answer 1

Without punctuation the sentence above makes no sense.

Si (no accent/tilde over the I) means "If"

Sí (with accent/tilder over the I) means "Yes"

Tu (no accent/tilde over the U) means "Your"

Tú (with accent/tilde over the U) means "You"

Assuming the comment above is supposed to read:

"Sí y no. Tú eres simpatica" means "Yes and no. You're nice"

"Sí y no tú. Eses simpatica" means "Yes and not you. You're nice"

Answer 2

It translates to "Yes and no, you are nice" in English. The phrase implies a mixed or uncertain opinion about someone's personality.