This is true for all relationships. Our closest relationships should always be to high quality people. They help us to become and to maintain our best selves. A relationship with those of poor character and questionable morals always drag us down to their level where they are comfortable. It's far better to be alone than to be with the wrong person or persons.

In the summer ?

Satan can't and won't be forgiven. Jesus was never an angel. He took on human form and died for humanity. Not for angels, fallen or otherwise.

I've no idea what a "common" demon is. The book of John tells us that Satan possessed Judas. A man that lived among the tombs was possessed by many demons. The disciples were sent out by twos, in part, to cast out demons and one they couldn't cast out tried repeatedly to injure or kill the host. In fact, we see in the Bible multiple times where the demon will cut the host. End time prophecies tell us that Satan will possess another. It is truly said that "we battle against the powers of the air." We battle against spiritual forces.

A person that steals without shame is very far gone. A conscience is a terrible thing to lose.