Reading the first page, it sounds like the OP is depressed, and needs comfort, not arguments.
I feel much the same way. Fatigue and depression weigh us down, but we gotta keep living anyway, and try to be happy and trust that it’s for a good reason. I think it’s also good to try to do your best, and then take some mental comfort knowing you did your best. There’s self-worth to be derived there: “I followed God’s will to the best of my ability. I tried to help other people.”
I’ve been planning to go to confession, but it’s just like, “Well, what’s the point? I’m going to cast another haughty eye or entertain lustful thoughts again.” I don’t even know if I have true contrition, even imperfect contrition.
I’ve been to Confession at times when I was utterly numb inside, barely able to think, not sure if God even existed. I was able to think, “Well, what I did wasn’t good, or wasn’t as good as it could have been, so if God exists, then yeah, I’m sorry I didn’t do better,” and then said an act of contrition (promising to amend my life, avoid near occasions of sin, etc), and that is enough, I think. We don’t need to “feel” anything; we just need to be sincere.
What exactly is human nature? Aren’t angels like pure, sinless beings? Why did God create us? Are angels not capable of love and free will?
Human nature is the state of being human: Finite creatures, we are our bodies and live according to our means the best we can.
Angels are spiritual beings who chose not to sin. (Those who did choose to sin are demons.) We can be pure just like angels – and we are, after Baptism and after Confession. We can live and die in a state of purity, as well, in which case we skip purgatory and go directly to heaven. Apparently there’s often an odor of sanctity or a supernatural expression on one’s face when this happens. See Corrie ten Boom’s
The Hiding Place, where – spoiler alert – apparently that happened to her sister, whose purgatory was a Nazi concentration camp. (Although otherwise an emaciated corpse, her face had a radiant, youthful beauty.)
Your last questions get to the dignity of man, which we don’t realize: We are of a higher dignity than angels – hence they come to help us (not the other way around) – because we must struggle with this physical world. Hence in the Bible there’s that part where I think St. Paul asks, “Don’t you know that we shall judge angels?” Our value does not come from our abilities (since angels have greater intellects than we do), but from what God has made us as: Human beings. This underscores why we must avoid sin, so that we can live befitting our dignity as Christians and as men.