Whats the appropriate time to wait after breaking up to get into a new relationship?

I was going out with this guy for a little over a month but it wasnt working out for me, and it didnt seem fair for me to keep leading him on when i didnt feel anything. So i ended it.
1½ days later he had a new girlfriend.
I know i’m the one that ended it… but is that not a little soon for him to be moving on?