The more I reread this chapter the more upset I get at Aiden...
Yes, he loves her, and what he feared would happen happened, and it would have happened no matter how he handled it.
So instead of having faith in the person he loves, he chose to be cowardly and only tell her after he had made her promise him she'd lose something important to her if she left him. That is extremely manipulative and Wendy is more than in all her rights to feel angered and offended.
If I were her, I would have been more hurt about how he treated me than for him being a different species altogether (prejudices and how "things" would work in between species aside).
The basis of a marriage should be trust, and he didn't trust her and has now made sure that she can't truthfully trust him either.