She doesn't think he realizes just how good she is at pretending. Because if he did he wouldn't believe that she truly had no idea about what was going on between Kitty and Bobby. But when she awakes to find that he's snuck in her room again it somehow doesn't matter.
He wouldn't try pushing her so damn hard to let him slither his thieving ass in her bed. She is all smiles and blushes when he runs his gloved hands over exposed flesh, sets her lips abuzz with kinetically-charged kisses: but despite all this she is terrified of what her mutation could do to him and he can't see that.
She can summon all the appropriate reactions and responses when he says he loves her, though she knows he's lying. He's said himself—back when they first met, back when they were just drinking buddies and friends and everything was simple—that he knew exactly what to say to a femme to make her his.
She can tell herself that when she turns and finds him looking at her with those pulsating eyes that he's really looking at her, not comparing her brown hair and brown eyes and pale skin to Bella Donna's golden locks and sapphire irises and bronze skin and dreaming about what could have been.
She lets him think he's fooling her because she needs him.