You are throwing three asserts out here that are not necessarily true.Do you believe that God would burn someone in hell forever for simply not believing in him?
Would you mind telling me what is so horrible about not believing in an invisible entity, that it merits eternal agony?
Eternal suffering for not believing in someone who is invisible and hides himself?
(1) You posit the belief that God punishes persons for "simply not believing in him." While you may find many Christians who profess that, if you pay attention to scripture, people are punished for committing evil and refusing the mercy of God.
(2) You posit the belief that God is "invisible" and "hides [H]imself." God makes Himself known to anyone who truly wants to know Him. Spend some time in the scriptures and you will see this. On occasion, He makes Himself known to persons who DON'T want to know Him as well, and it is agony for them. It is by God's grace that He is not eternally present for those who are unprepared to encounter Him. The veiling of His presence to those who reject Him is a temporary grace.
(3) You posit that those who reject God experience "eternal agony" and burn "in hell forever." While that position is quite popular in this era, it is not uniformly believed among Christians. Again, take some time working through the scripture and pay strict attention to what is said about who receives eternal life (only believers), the parables of Jesus regarding the fate of the wicked (they are destroyed, slain, burned up like chaff, etc.), and the way the Lake of Fire is described as "the second death." Those who reject God and do evil are destroyed at the end of the age. The suffering of Hell may be short or long depending upon the needs of God's justice, but it will end. God will destroy evil, not maintain it eternally in the Lake of Fire.
Your assertions sound like the opening salvos of an atheist who wants to upset the faith of naive and uninformed Christians. I have heard this stuff for years from many different people. The power of the arguments comes from the ignorance of the Christian who hears it, not any fault in the biblical revelation.
Perhaps you are the one who has heard them from someone else and are seeking help to resolve these things in your own mind. As a practical matter, I encourage you not to widely air these concerns with others because you will face a backlash from Christians who are weak in their faith and will attack you out of fear. Find one or two wise and experienced Christians and work through these things with them. Spend most of your time reading scripture (the whole thing, not just pieces) to get the big picture view before you settle on an answer to these questions.