What you are feeling (as you said) is jealousy, it is a passionate emotion but very temporary in most situations. Now think hard, if you two get back together, it wI'll be the same or worse as before. Even if she is a rebound, he is taking the steps that you should be taking. In the words of LdyGry, you should however, take time to yourself, at least a month of "me time" without any dating. Then take a month for each year that you two were together.
Also, spells like this, would just complicate things. Making matters from bad to pure hell. My honest advice would be to put him out of your mind and life, let these feelings pass, and let everything the was negative about your relationship fade as well. Learn from the mistakes you made in this relationship and learn re lessons that are to be taught from them. THEN start to go out and date again.