First of all, when God created this earth everything was originally good.

But God did make humans and angels with a free will. God wants us to choose to love and trust him, not force us. Lucifer, Gods highest angel in heaven chose to rebell against God, because he wanted to take Gods job: Lucifer wanted to be God. That was why God threw Lucifer and 1/3 of his angels who decide to join Lucifer out of heaven, on to this earth. Suddenly everything was not all good anymore, evil entered.
Now Lucifer:Satan was pissed and also afraid of God and decided to continue his plan in trying to become the King or God of this earth.

God gave Adam and Eve a choice: Were they going tu trust Him or the devil? We all know that Adam and Eve chose to listen and trust the devil. God saw that sin/evil would start to destroy all of his paradise and only bring suffer and destruction to this planet. God could have ended all evil that very second and chose not to create another human being ever again. But because He loved us so much he decided to give us a second chance and came up with this salvation plan. God has promised that one day soon he will put an end to all evil, but he wants to save as many as possible. He has also promised that he will make sure that after all the evil and sinners, including the devil and his demons have had their fair punishment and ended their lives in the second death, sin will NOT rise up a second time!

How can God be sure that this distrust and sin will never rise again?

That I believe is to allow the devil and sin to go on for a certain amount of period so that we will see how destroying sin and evil is in order for us to learn not to rebell against God a second time and to see that because man chose to listen to the devil in stead of God, we must see and experience the consequenses of sin. Most of the time suffering in this world are brought on by ourselves, because we choose to eat unhealthy, smoke, drink use drugs etc bringing illnesses upon ourselves. We let jealousy and hatred turn into obsessions in stead of trying to deal with them and turn to God for help and then quarrels, divorces, wars, murders happen. And often the faults we make because of our selfishness bring forward pain and suffering to innocent people. Also when we suffer it helps us to empathice with others and also in many situations it brings us closer to God, because we often seek him in times of trouble.

God doesn't cause suffering; Satan does. When we get angry at God, it's exactly what Satan wants. By blaming God for evil, we're actually following the one who IS responsible.I believe that evil forces attack us and cause much suffering in an attempt to get people to blame God and turn away from Him.
God gives us rights as individuals. Because He allows us to choose for ourselves how we'll live, He had to also allow us the freedom to sin. This means He had to allow the consequences of our behaviors, too. Some of those consequences are diseases caused by toxins, accidents caused by risky behaviors, and natural disasters caused by things like changes in the ozone layer, which we have brought about. Sometimes diseases and suffering are in order to show Gods strength in weak people, because God has the power and ability to turn weak people into champions. (David against Goliath). When evil entered the picture, it brought with it suffering. That is not to say people suffer because of their own personal sins, necessarily, but the world is changed, due to sin being part of the world.
Jesus said, "In this world, you will have tribulation."

We must also remember that God has promised that if we turn to him he will help us and carry us through the problems and suffering we face in this life. Also we have to remember that although God allows sin and evil for a short amount of period, he has a made a promise to make a new perfect world where everything is good. as in his original plan, only this time those who are saved will have learned their lesson, not to rebel against God and make room for sin and evil to enter a second time.