Question: “Why did God keep Satan around all this time and not destroy him a long time ago so that we would not have to suffer so much.”
Keep in mind that as much as Jesus Christ is the light of the world so is Satan the darkness of the world and those who walk in darkness are in Satan, and those who walk in the light are in Jesus Christ.
For ye were sometimes darkness, but now are ye light in the Lord: walk as children of light. Ephesians 5:8 KJV
To once have been darkness, it means to have once lived a life that was full of ignorance lacking regard to the truth, divine things and made ourselves colleagues with ungodliness and immorality. (Romans 1:21, James 4:4)
To become a light, it means to come to the full knowledge of the truth together with the spiritual purity that is radiant as the light and be associated with it. (Exodus 34:29, Matthew 17:1-2, 2 Corinthians 4:6)
If God, therefore, would destroy the enemy now that very destruction would come upon all those who are in Satan through their ignorance of the truth by believing in a lie and the practice of ungodliness (John 8:43-45). However, God seeks to save those who ought to be saved from darkness by His grace and convey them to the kingdom of His only begotten Son Jesus Christ (Colossians 1:13, 1 Peter 2:9). Thus God must keep Satan around for a while to cause His light to shine upon them that sit in darkness (2 Corinthians 4:6).
Through the tender mercy of our God; whereby the dayspring from on high hath visited us, To give light to them that sit in darkness and in the shadow of death, to guide our feet into the way of peace. Luke 1:78-79 KJV
God has set a time when He will destroy Satan (enemy) for once and for all (Psalm 110:1) but first, must the Gospel be preached throughout all nations then the end will come. (Matthew 24:14)
Therefore rejoice, ye heavens, and ye that dwell in them. Woe to the inhabiters of the earth and of the sea! for the devil is come down unto you, having great wrath, because he knoweth that he hath but a short time. Revelation 12:12 KJV
Therefore well-beloved of God, be forwarned to live a life on earth that is acceptable unto the Lord having nothing in common with that which is unable to yield what it ought to yield (1 John 1:6, Romans 1:21, 2 Corinthians 6:14-17).