sounds like shes cheating to be honest bro!
I had the same thing then she fucked my best mate..
Best idea would be to get all romantic, candles, incense, a little dinner and a movie, get into that notebook shit and get all lovey dovey n shit, obviously after 3 or so months of first dating you get over the honey moon period, then all of a sudden you become more and more comfortable and normal with each other, if you lose that lingo in bed or the compliments and sparks you have going on you'll never get laid.