Personally, I'd go with the e-mail.
I can describe my feelings best via writing, so I'd write an e-mail telling her exactly the problem.
For me it would go something like;
Hello!
So, lately things have been kind of odd. I guess it all stems from my bachelor mentality, and as I am seeking a relationship in the long term, it is going to take a hell of a woman to settle me down.
I see potential in you, but the problem is the jealousy (Forgive me if you were kidding). However, I am a single man, and until I meet someone wonderful enough to settle down, I intend to stay that way.
So we started off good, then I got the feeling you wanted more out of me than I intended (The text messages). And as I like you, I think you should know I'm uncomfortable with the way things are going. So I'd like to start over. Give me some time, and I will be the one to call you. A fresh start would be great.
Thanks for your understanding!
NemphtysWanderer the pimp.
This way she stops calling, and you don't seem like a jerk. Also, if you want to call her, it is still an option. Unless you want booty, then I'd write something like this;
Dear (Whateveryourname, cant remember, I was too drunk)
I've been doing a lot of thinking about us and so far I think you are great. There really is no problems I can see except;
I've been in some pretty serious relationships, and at the moment I really don't want to be in another one. But at the same time, my attraction to you is intense.
While I'm tired of the drama of relationships, I'm split because, well, to be honest, I want you in a bad way.
The problem with this is, I want to be with you, but I can also tell you, as soon as things get serious, I'm going to want to bail. So the attraction is there, and if we continue, I am not going to be able to resist myself. My warning to you is, I'm going to have a really hard time with any kind of commitment.
So if you understand this, thank you for being so thoughtful. I'm looking forward to exploring our relationship, but I thought you should know, commitment is not my thing at the moment.
Thank you;
Nemphthys Wanderer the sensitive.
This has worked for me a few times with girls I run into from high school, it is a nice way of saying, "I just want booty, and if you are really good, maybe we can do it twice."
And if all that doesn't work, and she calls and calls, you will just have to tell her to get lost.
Good luck!