Was I the rebound?

I am talking to this guy for a month now and he was in a 2-3 year relationship before me. And we follow each other on social media and he's got me as his wallpaper alongside with his mother who passed away. Anyway, we like each other but I've been seeing him reposting reels on his page that say "losing her was one thing but seeing her with someone else is another" and another was "deleting pictures of her but finding that one you took that was your favorite one". He said he broken up with her like 7 or 8 months ago,

I spent so much time with this idiot, and now I feel like I am the placeholder/rebound.

I dont expect him to not think about her but to repost Instagram reels about this said person while talking to me is cruel. I know we weren't together but if he said he liked me as much as he did why is he entertaining the thought of her? Was his feelings false about me?

Am I overreacting? Any advice?
Was I the rebound?
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