Ian looks at Wanda in Melanie's body and even he isn't sure if it's really her that he loves. He can't deny that this body isn't pretty, but that's not what makes him like her (he thinks).
This is the bad thing about falling in love with a Soul because you can never really be sure if you're falling in love with them in their packaging or not.
He is forcibly reminded of this notion when Wanda pulls her self-sacrificing act with Melanie's body.
He loves her for it, because it's so kind and so selfless, and he knows that it's real.