You described a chapter out of my earlier life.
The reason she's now trying to control you is because she knows that other women are bidding for your attention. Women are very perceptive In fact, for every clue you missed from an outside woman, she didn't.
Your mileage may vary, but here's my story.
In college, I met someone that I was very in sync with. Compared to past girlfriends and dates, she was in a league of her own. It was also around this time that I noticed that I was turning more heads and getting more attention from a higher caliber of women.
My girlfriend's best friend looked like the cheerleader type (which I never had when in high school). The new sudden possessiveness of my girlfriend and the prospect of bedding this 'cheerleader' type ... well, you can get what happened.
I became single. Suddenly the 'cheerleader' girl wanted nothing to do with me. At first I was surprised, but the reality is... she had a challenge and she achieved her goal. On the other hand, I developed a revolving door with other women and it almost seemed like a twilight zone episode. Before I would consider myself 'average' with the girls, but now, things were happening like I would have never imagined.
After a while, it became boring. Sure, it was nice having new 'strange' and all, but they were not interesting beyond that. And as it's been mentioned here, the more disinterested I became, the more interested they became. Forums like this weren't around back then and it really did seem like I was living a twilight zone episode.
I'm now in my 50's. I've got a lot of bedpost notches (and I don't regret that). I've also had countless relationships since the woman I cheated on. However, there's only been two since that woman that truly held any actual value.
If the woman you're with was a result of being a position-filler, then you'll probably enjoy this new adventure. If she is more than this, you could regret it.