The whole situation was formidably cruel.
This is the natural state of the world. The fact that it's so abhorrent to us now is a testament to how far we've managed to come.
I’m not sure how you could ever think that love is somehow the a priori concept of the world. Do single-celled organisms “love”? What about insects?
The answer is no, and evolution tells us what this cruel world is all about: propogation of genes through sex. We, as beings, are irrelevent: just hosts for a game that is being played at a different level.
Animals also take care of their young, they often mourn those who died.
Plus, your incredulity at the thought of "love" between single-celled organisms is without basis. Love is a subjective state which we can only infer. We (well, some of us, not you I guess) think it's real because we've felt it at a level to which to describe it as not real would do violence to our conception of real/unreal.
And then we infer that it's felt in other organisms around us based on their actions.
Now, a single-celled organism really doesn't have a great range of "actions/behaviors" it can show us. Therefore we don't get to see it. This says nothing about whether it's experienced or not.
Many animals also eat their young. Taking care of their young is just as ingrained in their evolved behavior as eating them.
Otherwise, I agreed with the rest of your post. The whole "do <x> organism 'love'" concept is a bit of a mind bender as usual.
Animals also kill their young on purpose, including people.
Do your cells in your eyes and in your butt love each other? If so, you have a pretty flexible definition of love.
Of course love is a thing, but is a much more recent phenomenon than pain. This is why it's much easier to feel pain, that in it is to feel love.
Humans and elements have a "S-shaped" function in which they rather avoid pain than feel pleasure. Would you rather feel a lot of joy for an hour or not be tortured for an hour? Most choose the latter: the stick is more powerful than the carrot.
I think it's a little disingenuous to that animals feel "love." Neurochemically, it's a little unclear as to what the feeling of love even is. Pain, on the other hand, is quite clear.
Therefore, we can reasonably conclude that pain has been more of driving factor of evolution than love. And then in it also follows that pain has been more prevalent than love in the history of the world.
Careful there, you'll bring out a whole cadre of people dragging you over the coals with that sort of opinion. They'll call you "godless" or something else, which translates to "I can't debate your opinion, so neener-neener".
But if you interpret the "natural state of the world" to include loving parents, but not decent medical or agricultural technology, life can be "solitary, poor, nasty, brutish, and short" in spite of parents' love. Or even "formidably cruel".
Do you think you would be more likely to sell your children if you had 8+? Or if you were dirt poor? Homeless? Addicted to drugs? Starving? On your death bed?
Bringing another being into this meatgrinder of a world is the cruelest act in itself. Everything else is just a matter of degree.
My world view is grim, but not as pessimistic as yours. May I recommend you something?
Have you seen the movie Arrival? The protagonist makes a decision near the end of the movie that is as much in contrast of your statement as it can be. I was (and still am) unbelievably moved by that revelation and think about it to this very day.
They didn't have birth control.
I grew up in a world where my parents used it, I use it, and my grandmother guilt tripped my grandfather forever for not telling her about it until after they had three kids.
Forever, meaning she still brought up the issue when I introduced my wife to them.