@Jacob
It's one of those interesting philosophical questions that can't be answered without humanity meeting a new sentient species that we can actually communicate with.
If we found another form of intelligence in the universe that we were able to make emotional connections to, relationships are practically guaranteed.
Think of it this way, though.
If any relations with non-humans is automatically immoral, no matter what, then Captain Kirk is doomed to hell.
He got quite a lot of alien tail.

He could be in this very room! He could be YOU! He could be ME! He could even be- User Banned