Can we just take a step back for a moment to reconsider the words you're using here? Regardless of what aspect of nature we are discussing, I think any argument about nature that includes the words "designed" or "construct" or "requires" is doomed to fail and is flawed at the most basic level.

Nature is something we observe, not something we impose our own desires and prejudices on. It obeys the laws of physics, laws which we have abstracted from many observations. These "laws", or really we should just call them abstractions of our observations, help describe what we observe. They "govern" chemistry and thus biology. We are really just a bunch of molecules interacting with each other. There is no purpose or intent that we know about and can prove, just observations about how things have been working.

Homosexuality is natural. It's just a thing we see in nature. It's not inherently good or bad, it's not the inherent root cause of diseases or anything like that. It's just a biological variation. It only becomes bad when society arbitrarily decides it's bad or worthy of judgment, and that's because someone's religion says so or because someone has a fundamentally flawed view of how nature works.