Hi, it's good that you are confronting this issue at such a young age! I settled down really young, and it didn't go too well! I think a commitment issue can swing both ways (undercommitting AND overcommitting).
I might be wrong, but the way you describe it, I think the chasing sex issue could be a secondary issue. You said it's maybe about validation?
Have you thought about speaking to a therapist?
These are probably very common issues, but if it's troubling you, it could worth be seeking professional help.
What are your personal reasons for wanting to make a commitment (not to do with the girl)?
And do you have personal reasons for not committing (not to do with other women)?
There is already something you feel unable to talk to this girl about, which doesn't suggest you two are communicating very openly. Do you feel you share enough values to make it work long term?

Also, sorry to be very blunt but...horny and needy aren't really emotions
Are there specific things about the idea of new partners, and the idea of commitment that make you anxious or excited?