Keep it real.
Again, there's a difference between being emotionally nonchalant and being a total d-bag. Treat her with respect and kindness, but never woo her with insincere emotions.
Strike "I miss you" from your vernacular if you don't really miss her, and you only miss having sex with her. Clearly, there's a big difference. Don't tell her she "means so much" during pillow talk because it feels good to say and you want to see her smile. Honesty will make her happy. You can keep your half-ass compliments and sweet nothings to yourself.