Is he in a rebound relationship?

Me and my ex broke up in August. He promised me he wouldn’t date another girl especially since we were forced to break up. He also said he loved me very much and he couldn’t handle being in a relationship with me. A month later, I see pictures of him and his new girlfriend. I’m upset because he lied to me. Why is he doing this to me?

Is he in a rebound relationship?
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