Text original - Polonès - hej eva

Hi!
I have a question about this sentence that is submitted for translation. Well, if I translate the beginning of a sentence "Ja naprawdÄ™ nie mogÄ™ byc tobÄ…" EXACTLY from Polish into e.g. English, then it means "I really cannot be you" which in Swedish is "Jag kan verkligen inte vara dig". My question is: shouldn't it be: "with you" ("Jag kan inte vara med dig" = z tobÄ…). The little preposition "z" in Polish = "with" is perhaps missing or am I getting it wrong? Just a feeling about the sentence an a context, and I prefer to ask first instead of translating it in a wrong way...
Thankful for help..
Katherine