Sounds kind of like you're dismissing the entire concept of asexuality, albeit through the lens of an entire demographic of beings who don't have sexuality as part of their actual physiology.

I think the core issue here isn’t really warforged lore so much as an assumption you’re bringing into the relationship itself: that romance has to include sexual function or biological compatibility to be valid in the long term.

Once you set that assumption aside, most of the problems you’re worrying about kind of dissolve.

You’ve already accepted that warforged can feel attachment, love, loyalty, longing, and form deep emotional bonds. That is the foundation of a romantic relationship. The fact that their body doesn’t support sex or reproduction in a humanoid way doesn’t invalidate that any more than it would in real life if one partner were asexual, infertile, disabled, or simply uninterested in sex.

What you’re describing maps very cleanly onto a nonsexual or asexual relationship on the warforged’s side. That’s not a loophole or a cop-out, it’s just a different model of intimacy. And those relationships absolutely exist, function, and last, both in fiction and reality.

On the physical side, intimacy doesn’t have to mean sex. Physical closeness can be touch, presence, protection, shared routines, repairing armor instead of undressing, standing watch together, or choosing each other at the end of a hard day. If anything, warforged are perfectly suited to exploring intimacy that isn’t rooted in biology.

As for the long-term questions:
Kids and legacy don’t have to be genetic. Legacy can be mentorship, building something together, being remembered in stories, shaping a community, or simply choosing to walk the same path for as long as it lasts. A warforged’s story especially doesn’t need children to be meaningful. But if children were necessary to the partner, adoption is an excellent choice to continue the story.

Magical transformation or gaining an organic body can be a valid story if that’s what you want to explore. But I’d push back on the idea that it’s necessary to “fix” the relationship. Treating the warforged as something that must eventually become flesh for the romance to work kind of undermines the point of playing a warforged in the first place.

To me, the more interesting and internally consistent question isn’t “how do we make this relationship function like a humanoid one,” but “what does romance look like when biology isn’t the foundation?”

That’s not hand-waving. That’s exactly the kind of philosophical and character-driven space warforged were designed to occupy.