I went out with this boy for 11 days and he dumped me saying he wanted to be single then 2 days later he asked my best friend out did he use me to get closer to her?

It's a possibility. He doesn't sound like a fantastic guy from that summary though, so please don't let yourself be too cut up over him.
How old are you?

Kal

I am 15

I wouldn't worry about this. Take this as a lesson learned and go on with your life. Now you know what kind of people are out there and you are better of without him. Now regarding your best friend if she really is your best friend she will be smart about this and realize what happen to you and will not do anythign about it. Time will tell.

Just be glad that you found out what he's like early! Don't waste anymore time on this jerk

I know at 15, 11 days seems like a big deal but trust me in 11 years you won't even remember this guys name or these 11 days. Take it as a learning experience and learn to be slow and patient with new people in your life.

Think of it more like this... you just experienced in 11 days what NORMALLY takes 6-24 months to occur, I call it the natural life of a relationship:
You like each other
Spend some time/perhaps even exclusive
It gets old in some way
Someone moves on and the other person is left hurt and asking self-doubt questions
You're going to experience this over and over, so recognize it as the learning process it is.

Yeah, he may have used you, but this isn't about him, it's about you. You learn stuff in every relationship, even ones only 11 days long, even ones that may have been false from the start. You learn, every time.

So, make sure you learn. Think back over your time together and make notes about what was probably real and what was not. Keep that in mind next time. Don't punish future boys for the sins of this one, but keep those sins as a reference and know the warning signs. That's learning.