Have you ever heard of a "rebound relationship"? Many people will break up, and then get together with the first person to come along just to be with someone again. Rebound relationships rarely last, because they usually aren't built on a real connection.
Anyway, another thing you need to learn about relationships is that, once they are over, you need to NOT CARE what your ex does. He is your EX, which means he is free to do whatever, including make huge mistakes. Don't let your ex's affect you.
One month is not usually enough time to take before starting a new relationship , it isn't for me anyway. After my first Divorce it took almost 6 months to go on a date , much less want a relationship. If I was to make a guess I would say , rebound