I mean, the desire to have a kid with the one you love the most, and starting a family and stuff, that sounds pretty sweet. We can already tell that Girly's childhood is great, so of course he would picture his ideal love and family in the future as the one he had. And from his backstory, we can also infer that he might have this 'destiny' wish stuff partially because he wanted to give his child in the future a complete family, the traditional way, with a mother and a father because he lost his mother so early.
Yaoi/transgender het may still happen, and it's very likely, but it's still understandable that his wish of a partner and a child won't be going anywhere anytime soon.
Mother nature already called it, and a new human life can only come from a male and a female...so his wish will be directed that way. And since I doubt that science can develop in this manga (not to mention sperms are much harder to combine because they really lack the materials, and there's a reason millions of them die before reaching the egg. Call it a selection process.)so perhaps they'll look into adoption, since a complete family doesn't have to have that kind of blood relation. Destiny is a strange little thing, and it's never something you can tell, and I'm sure even Girly has no clue. He just believes that falling for a girl is in his destiny, but when he feels it eventually, who knows what will happen...
Thanks for the translation! This is really amusing and mysterious so far, and hopefully Kitano can work things out eventually. Girly may fall for more girls and femboys in the future, but you'll be here for him every step along the way!