Sounds like you're projecting something on not being a parent. Try the "what for" game. What do I want kids for? To extend my legacy. What do I want to extend my legacy for? To feel connected to the world. What do I want to feel connected to the world for? Just keep going recursively until you deconstruct it to a point where you see that it's not as bad as all that.
I don't know why, but your story made me think of volunteering. Have you considered it? Might give you a sense of motivation and meaning.
Also, since you seem to be in a fragile state right now, very regular outdoors or not-at-home exercise might be a good way to get mental balance.
I'm assuming that people have a biological imperative to reproduce. That matches what I know about biology and evolution and it explains why people so frequently have kids despite kids being, on paper, a rather poor deal. The "what for" is just "This is my fundamental nature."
I think that you can't really examine your out of a fundamental drive. You can't scratch the itch by asking "what for" any more than you could convince yourself that the fire wasn't burning you by contemplating why your hand hurt when you put it in the fire. Most people just want to reproduce as an end goal to itself.
All this said - I tend to think OP's problem is more psychological / depression as others have commented. If it were truly a strong desire to have children than OP would have simply figured out a way (adoption, in vitro, getting with another woman, surrogate, etc). Instead, it might just be a manifestation of depression - which is why OP just suffers from the desire rather than attempting to fulfill it.
> I think that you can't really examine your out of a fundamental drive.
It's a problem to label something a fundamental drive, because you're implicitly saying that someone experiencing it is powerless. What if it's not fundamental? You think so, but you might be wrong. Let's just call it a desire.
Btw, kids on paper being a bad deal is a bold statement. For thousands of years that was the primary way of investment. Between the ages 13 and 16 a child on a farm would return all investment required up to that point.
And, as for biology, I'd say that the primary differentiator of the human animal is just how flexible it is in the face of desires such as this.
I don't know why, but your story made me think of volunteering. Have you considered it? Might give you a sense of motivation and meaning.
Also, since you seem to be in a fragile state right now, very regular outdoors or not-at-home exercise might be a good way to get mental balance.