Hi Joana,
Your ex may have said that to your current boyfriend because he may not want you to be happy with this guy.
This is especially likely, if your ex is currently unhappy.
If he hasn’t met anyone that he wants to be with, he may be bitter.
As a result, he doesn’t want someone like yourself to have happiness when he hasn’t found any for himself.
Sometimes, there is a competitiveness that some exes who go through a bad breakup have with each other.
They don’t want their ex to meet someone and be happy before they have had a chance to meet someone and get happy first.