Impregnation (explicit)

That's a highly fascinating situation. I can't tell if you're larping or not, but if you arent, what a bizarre idea. I'm curious to see how it works

All those unnatural ways of making babies are completely condmend by the Catholic Church and think its even an excomunicable offense. I think Humanis Vitae talks about this for example, and the catechism of course.
Adopt a kid if you really want kids.
Anything else is an offense to the human life and the dignity of the embryo or outright adultery like making a baby with a donor, making that child a bastard.
Only through the love of parents during the sexual act a life must be formed, not with the help of a third party in a lad who treats embryos just like some biological material.

Love isn't all about just liking of partner physically.
But you really need to have relations with her to have kids.
Although in your case I wouldn't do it because kids should have parents that really love eachother in a marital way.
The best for you and your girlfriend is to live a life of celibate and live like brothers if you wish, since you guys don't feel attracted to each other.
I'd avoid having kids because of a bad example and suffering that might cause in their lives.

Abraham and Sarah, Zechariah and Elizabeth, others - couples who thought they were infertile but conceived anyway because it was the Lord's will, not by by finding a third party.

Onan didn't masturbate, he pulled out of his wife's sister and 'spilled his seed on the ground'. Masturbation is thus inferred to be sinful, because by jerking off you too are spilling your seed upon the 'ground'; ground here referring to any place that isn't inside a woman (i.e. your sock still counts).