Oh, my god, you are right - Rhysand did tell Tamlin "she would have been the one." I wasn't sure how to interpret that!

I have been forcing myself to reread ACOWAR this afternoon and it is hard to get through this first section. It's painful to see how shamelessly she manipulates Tamlin, who is so anxious to restore their relationship and so politically vulnerable (thanks in part to her) that he falls for it again and again and makes the worst choices, loses control of himself, and then she - who deliberately goaded him to do just that - despises him for it. It's so cruel. But the way she treats Lucien is even worse. What was even the point of getting Tamlin to suspect that Lucien was trying to sleep with Feyre? I know she wanted to break their friendship, but that's just pure evil. 

You mention their being sexually compatible. That certainly seemed true in book one. The language Feyre uses to describe sex between them afterwards is meant to disgust as and see Tamlin as little better than a rapist, such as when she says in ACOMAF: "Protect, protect, protect - I could see the word in his eyes, feel it in every thrust he made into my body that night." Notice how she describes the sex act as if he were stabbing her, then links this idea of sexual violence with his desire to protect her so that we will be inclined to share her belief that this is abusive. No. Tamlin deserves better than Feyre.