Why do I gradually lose interest in a girl as I continue to have sex with her until I no longer want to see her?

It's happened with the past 4 girls I've been with.
We'll start talking and I'll have some general interest in them that lead me to them in the first place.
After chatting for a bit, we'll meet and either have sex the first night or second/third. The sex is pretty good, and I spend the night or they spend the night, then morning sex! So things go pretty well, but I've started to realize with each girl, that after having sex with them, it's like a meter of interest I have for them. If we have sex, it goes down. Slowly, gradually but indefinitely. After about the sixth or seventh time sleeping together, it gets to a point where I no longer have any interest in seeing or even being around the girl.
I actually just got finished having sex with the most recent one. She came over for a movie night, and we had slept together about three times before. The first time, she blew me away. Great body, lots of common interests, we had a good time together it seemed. This time though, throughout watching movies on Netflix, I just knew we were going to have sex the entire time, and as the "time" got closer, I wasn't exactly enthusiastic about it, it was more of a "Cool, sex. Guess I'll go ahead". And afterwards, I cleaned up, walked back into the room, and saw her still laying in my bed. I started getting dressed and she asked "Why are you getting dressed..?". I knew this was her way of saying isn't there going to be a round 2? But no, I wanted her gone, to be completely honest. I guess she got the message, and started getting dressed. I was going to walk her back to her apartment, but she simply said, "I can walk myself back" and stormed out.
I can't lie and say I wasn't relieved that she left, and I'm pretty sure she won't want anything more to do with me, which I'm not upset about.
What is wrong with me? Why does it seem that I can't make some sort of meaningful connection with women? It seems like sex is all I'm able to accomplish, then I lose interest and don't care anymore. I don't want to feel like this towards women I talk to.
Edit 1: I didn't expect this to blow up overnight. I appreciate everyone's input over this situation. A few things I'd like to add from what I read so far:
I agree with this statement completely. I've had many nights thinking and wondering to myself what the issue is. I've come to the conclusion that I'm having sex far too quickly. My perspective on it is that sex, at least for me, in the dating sense, is the end goal. Sex drives you to want to know someone and get to know them more. Obviously, there are other factors like common interest and comfortability, but I feel that sex is usually that motivating force behind wanting to go all out when meeting a girl. The fact that I have sex with these women the first or second time we meet, basically ends that pursuit for me. I've 'won' the race, gotten the cookie. What point is there in continuing to try and get to know them or build anything more when I've gotten the prize?
Something else I've definitely thought about, and quite frankly, I have no excuse for NOT doing other than that I may be addicted to the sex. If not addicted, I don't have the proper self discipline and control to deny it, especially when the girl makes a move. Even if prior to us being alone, I tell myself, "This time, THIS one, I won't have sex with outright. I'm going to wait and get to know her first". All it takes is for her to start rubbing on me, and that thought goes out the window.
I don't believe I'm still 'in love' with my ex. The break up was 2 years ago, and what I went through truly opened my eyes to a LOT of problems and issues I personally had in my view of relationships and life in general when it comes to people. I've grown exponentially from where I used to be when dealing with my ex. I'm not however, against the idea that the **** storm that was that relationship is in some way affecting my behavior with the girls that followed afterwards.
I saw a comment in here, Jason1009 "You haven't met a girl that strikes your fancy for anything more than a few ****s. It's common. I openly admit that there is a HUGE gap in woman I would just **** or woman I actually want to be around for a long period of time and as time goes on, the gap widens."
I can also agree and admit that there is a gap for me. The girls I'm attracted to physically, I try to find some common interests, like with the girl from last night. We both love horror movies, watch anime, have the same favorite shows. I know it isn't anything to build a relationship on, but those were what I latched onto to justify being around her and spending time. Because we both like watching the same thing. It sounds ridiculous typing it out actually, but I can confidently and honestly say that out of all these girls I've been with, I had a specific point where I thought to myself, "I don't see myself being in a long term relationship with this person.".
All of them. Every single person. This whole issue may be as simple as I'm not going out of my way to go after the girls that truly capture my attention, and I'm settling for the ones that look good to me and I'm lusting after, but don't have any general interest in other than sex.


Source.