Why does my ex contact me?

I've been on this roller coaster since we broke up last August. The relationship had it's ups and downs, but even after the break up, we still continued to act like a couple. It all can to a head this past halloween. I became crazy obsessive with her. Got jealous, constantly asked her if she was dating anyone else, etc. It was none of my business, and she said I became too obsessive, and that she didn't want to ever talk to me again. I realized I had some problems of my own to deal with, so I began seeking therapy. I learned a lot about my low self esteem problem. After 19 days of no contact, my ex started texting me like crazy, and even called me that she wanted to see me. I was weary because I had finally started healing, but met her anyway. She had some problems she was going through, and said realized I was a great guy. Part of the reason she wanted to see me is because she missed and enjoyed our intimacy, so we have . And a lot of it. This was a month ago, and slowly, things are going back to the roller coaster ride. I will admit, I don't do any of the things that made her break up with me (pive aggressive, obsessive, constantly asked her where she was., etc.) and still give her space. In fact, she initiates 90% of the conversation, and when we do hang out, I'm constantly trying to be the man that she wants me to be. I try to be romantic, etc. Just doesn't seem good enough. She tells me she has feelings for me, etc. But, for example, our last form of communication was her calling me actin all weird. I ask her if she's back in the mode where she doesn't want to talk to me, she replies "kinda" then gives this whole speech about how we've been broken up for 4 months, but still continueing like we're doing. I respond, we'', you know what I want. She wanted me to repeat it, so i told her I want her back, saw a future with her, etc. She said sometimes she doesn't see the same thing. So I let her go. Half hour later, she asks if I have plans, asks if I want to do dinner, then asks if we can hang out and watch a movie at my house. When her movie ends, she says she's tired. I get up to take her home, but then she's already halfway to my room, strips down to her underwear and sleeps in my bed, asking me to hurry up. Nothing too intimate happend. The next day, I try to suprprise her with breakfast in bed, she doesn't seem appreciative. Then she gets all quiet, won't communicate with me, and wants to be taken home. And I haven't heard from her in a few days. I did ask her if she was only hanging out with me until she found something better. She said no, she's not on the market to find someone new.