Satan was on to Christ just before Judas was to give Christ over.  At the Crucifixion, Satan and his demons saw the blood and shrieked knowing that It was Christ and His Blood was Saving. The demons were to fly to Hell, but Our Lady asked God that they stay for awhile and then let go to hell.

When Christ was tempted, Satan was not sure if Christ was the Son of God.   "If you are the Son of God"

This is mentioned in the Mystical City of God.

Absolutely false!
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Matthew ch3
 And the unclean spirits, when they saw him, fell down before him: and they cried, saying: Thou art the Son of God. 
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 Mark ch 1
 And there was in their ѕуηαgσgυє a man with an unclean spirit; and he cried out, Saying: What have we to do with thee, Jesus of Nazareth? art thou come to destroy us? I know who thou art, the Holy One of God.  And Jesus threatened him, saying: Speak no more, and go out of the man.
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When satan tempted Jesus, it was only to his human nature and will that he could appeal, even though he knew Jesus also to be God.
 

Confused and worried,

Hebrews 5,6 speaks about if you repent and then turn away from God, there will be no more sacrifice left for you from heaven and it would have been better for you to have not know the truth.

I have repented and come back many times. I am back. For good.

I am worred, I've messed up.

This is why Jesus instituted the sacrament of confession. He knew best what we need. When you mess up again then get up and go to confession. 
I will pray for you. 

I have read this before and I was told by one of my Theology professors that until the Crucifixion satan wasn't sure if Christ was the son of God. That is why the Pharisees were telling Him to come down from the Cross.

Your theology professor was wrong.