He knew that he was still emotionally attached to his ex and thereby emotionally unavailable to anyone else.
This means that, regardless of whether it was you or some other woman that approached him, he most likely would have wanted the same.
Just sexual relations.
Keeping this in mind, it wouldn’t be prudent to keep blaming yourself or thinking that he must have thought that you were an easy girl.
He would have looked at any other girl in the same way.
You happened to approach someone who just wasn’t emotionally available.
That was not your fault.
When we take a chance on approaching someone, we never really know what we are going to get.