St Maximus makes a distinction between 'being' and 'Well being.'
Every rational creature (human or angelic) has 'being', and this never ends, but only those rational creatures that choose to participate in God have 'Well being,' which is not only endless, but beginingless.
God is beyond being, the term does not apply to Him, only creatures. Being has a beginning, and every being is limited by this, but those creatures that choose 'Well being' are granted an eternal beggininglessness, as God has, and so they do not exist in such a limited way, but partake of Gods limitless existence, and know reality, in part, as He does. Only He really knows anything, so this is the only true way to know anything worthwhile at all. There are varying degrees of this, but the saint tells us that when we have faith (not just a set of beliefs in our mind, but active conscious faith, as an internal action or movement) we connect our spirit to God as far as we are able, and the more consistently we do so, the deeper the connection will become.
God will not revoke a creature's 'being,' and as long as it is possible, he will grant 'Well being' to those who request it, and work for it. God desires 'Well being' for all creatures, this is what they are designed for, but a free choice must be made.
All evil is defined by St Maximus as misuse. 'In all things misuse is sin.' That's what he said. It's the best way to look at sin and evil, a privation of good, by unnatural use. Everything has a use and purpose, or a wrong use (or maybe a few of them). Virtue is right use, sin is wrong use. Simple, except when it comes to our minds.
Remember the passions are not just of the soul, like anger, lust, despondency etc. But also of the intellect - forgetfulness, ignorance, pride and such.
When we try to understand theology with our minds in a passionate state, forgetful of God, proud and self-trusting, we misuse our minds and end up with imaginary fantasies about things that cannot possibly be true, because if they are able to exist in our limited minds it stands to reason that they cannot correspond to a spiritual reality that is beyond the mind and above our perception. In this way, any adherence to a purely logical and rational understanding of spiritual reality by necessity, ends up denying that reality, by limiting it to our understanding.
By opposing the intellectual passions with prayer, watchfulness, filtering of thoughts and humility for our limitations in understanding, truth is revealed beyond the confines of imagination and logic, and this is when we start to experience 'Well being.' There is less mental turmoil, more love and peace, when the mind gives up trying to comprehend things outside it's ability, and takes it proper place beneath the spirit.
It's actually a lot easier than trying to figure things out with thought and imagination because truth is natural to our spirit, while imaginary and rational concepts are for the purpose of navigating the limited sense world in the body, via the soul. Thinking, imagining, creative type or critical mental work is meant to be applied to the sense world, for our survival and helping others. It is not for theology. The spirit knows theology by direct experience, beyond any thought or idea, it is the beginningless knowledge of God, through His energies (grace).
Also, the less you abuse the mind by trying to discern spiritual truths with it, the more useful it becomes for it's right purpose; like writing, or organising, or designing things etc. Grace flows through the spirit into the mind, soul and body and they work together as a team for the Lord.
Your mind and intelligence is pretending to do the job of spirit, and that is the primary task of the Devil today, to encourage us in intellectual passions and the misuse of reason (and all the rest,) so we fail to perceive, beyond mental limitations, truth as it is flowing from the Truth Himself. He wants us all tied up in ideas and imaginings, the tools of the world, killing the spirit that seeks knowledge in a friendly participation not a grasping comprehension.
If we doubt the devil's existence, all sin and evil is instigated by man alone, and there is very little room for mercy. You can see how cold the world becomes when the devil is forgotten. Resentment and revenge, and the worst of sins reign, as so few see behind the veil to his machinations, but hold grudges without end and literally hate their own species for it's 'satanic' nature. Seems counter-intuitive, but history proves, cultures with firm belief in the devil, and his wiles, have more love and fellowship and stronger familial ties than those that reject him and look for human or in inherent evil.
The Devil has forever forsaken 'Well being'. He can only limit creatures to misuse of themselves by suggesting ideas and deeds, restricting them to mere being, like animals. God allows us to be tempted by him in mind and through our environment so we can choose a side, and to teach us the way of warfare - how he tricks us, and to learn humility also, when we fall for a mind-locking finality about anything that leaves us cold, or a fleshly desire or something. Remembrance of God banishes the Devil, but not always straight away, it can be hard. It depends on God's will for us, and our good intention.
As for God being responsible for evil, what you are really saying is that God can't handle evil, but that may be because you haven't let Him handle you yet, by really giving your spirit a chance to inform your mind and soul. Or perhaps, like some other people, you are tempted to think that evil is okay, and is from God, because you can't mentally comprehend how it fits with a loving God, and your definition of love, or perhaps seek a theological justification for continuing to enjoy it without guilt. This is just New Age, like the book 'Conversations with God.' It's an old doctrine called Gnosticism, an admission of defeat and a limiting of everything to human understanding. It should eventually result in a very boring and numbed world. Most of the people where I live hold to this belief, and trust me, it's boring.
I would just fear and pray to God, respect and fight the Devil, trust the Church Fathers, be internally honest above all - all the time. 'Knock and it will be opened unto you,' Christ promises, so how can we fail? Just keep knocking.
Thinking isn't knocking.