Is it a rebound? Or am I just being stupid?

Please bear with me. I could really use some help.

My ex and I dated for 2 years.. he was so serious about me and I was going to leave for university.. we knew that from the beginning and he was always convincing me about long distance. However, after joining a local college, and I'm on a gap year, he changed his mind and we mutually ended things (I didn't really want to).

When we met to break up, he was strong but upset and said he doesn't wanna date until graduation and wanted to be friends. He met me once after that while I was with my friends, and called once/twice. He mentioned liking some girl a month after we broke up coz i asked. 2 months after the break up, I found out he already got into a relationship a week after we split. He told one of his friends over chat how he is "chilling with his girl" and that they've been together for like a month.

He seems to have had this whole thing prepared. Its so shocking because he was never like this. And he's more active online/socially. He already has her on his display; he never cared much about his display before but now he suddenly does. I don't get how he jumped onto the next girl so fast.. And he lied to my face so many times, even when he came to meet me, and said he isn't dating anyone..

Is it a rebound? Or he liked her from before and was very prepared for the whole break up and planned it through..
Is it a rebound? Or am I just being stupid?
Add Opinion