SOLVED. SciFi - Alien - Subtle invasion, not typical alien, look like humans, create human/alien offspring. [s]

[Riley]

This is a SciFi and MAYBE YA book. Not sure on that part. Mass market paperback was probably 300-400+ pages. I read it in the early 2000s as a teenager. Cover was a dark blue and I want to say the title was something to do with Invasion or a synonym. Not a long title, 1-2 words tops (I think). The aliens are more like humans, as in not your typical alien. Not recognizable.
Sort of Spoiler: There is a chapter where an alien and human have sex and I want to say it is in a shed (weird, but I'm pretty sure of that). It is strategic, not a fetish type thing. The idea is that the alien creates a human/alien baby. I could be wrong but I feel like the alien offspring becomes a moderately involved character... Not entirely sure...
I can't remember much, it's been so long. Anything helps!

[Kris]

Riley, can you tell us more about the main characters?

Is romance an important part of the story?

What's the location - country, region, big city/small town?

[Riley]

Not high on a lot of people's interested list but I was cleaning out my dad's basement and found the book. Taken by Thomas H. Cook - https://www.goodreads.com/book/show/5...

[Kris]

Great. Glad you found your book, Riley. Thanks for the update.