Why is my ex acting this way?

Hi. So, I found out that only a few days after our break up, my ex started sleeping arounds with many girls (and doing drugs) ! I know he's my ex and that he has the right to do anything he wants, but this just makes me think that our long- term, loving relationship meant absolutely nothing to him. He broke up with me saying he needs time alone, that he wants "free life" and that he doesn't love me anymore. All of a sudden, I woke up one day and he told me exactly those words. It didn't end well. What do you think, if he was ready to sleep around just few days after 1 year old relationship, did he even care about me if he replaced me just like that?
Why is my ex acting this way?
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