The spelling is "estoy", not "estoi". That means "I am with another [woman]." The word "woman" (or "girl") is not explicitly mentioned, but that's what it usually means; in any case, it must be a feminine word.
Yo estoy con otra means "I am betraying you with another" in Spanish. This is likely a portion of a song or could be the lyrics to the song that is called "Te Estoy Enganado Con Otra."
The Spanish word "con" translates to "with" in English.
"Con quien estas" translates to "who are you with" in English.
Se escribe con you con acento
no hable con maria
"Con frecuencia" in English means "frequently" or "often".
"Dios con nosotros" translates to "God with us" in English.
It means with you.
Con quien means "with whom"
Conmigo means with me.
Dragonfly
With reason/rightly