It's more like he's in love to a dryad... the spirit of a tree. Trees and plants are living things with a soul, so it's not weird to fall in love with it.
Notice when you see something beautiful, like the sunset perhaps, or a view so magnificent and beautiful? The feeling you get at that moment is like falling in love right? It's because you see the Life in those things, and if there's life, there's a soul... Souls are just like a concentrated essence of life, so anything with life has a soul no matter how small... Some of those souls receives consciousness, like spirits, and most spirits has physical forms, like humans and animals and plants.
And this knowledge has been around long before us, since life started before us. It is simply that, we tend to disbelieve anything that wouldn't fit into our individual reality.
what is this world coming to