Rabbi, can you help me with a question? When God told Adam to leave the garden of Eden, did God say that you (singular) must go or you (plural). Was God talking to both Adam and Eve or just Adam? 

Excellent question!

The answer is that although it is written in the singular form, the word "Adam" also refers to mankind as well. Hence, since Eve, Cain and Abel are all part of mankind, they were all exiled from the Garden of Eden. (Source: "Aznayim L'Torah" by R' Z. Sorotzkin, Genesis 3:24)