Is my ex still upset/hurting or is he just uninterested?

Several months have passed since our break up and today I messaged him saying I’m ready to be friends. All he replied back saying is that he’s been told by my sister not to be in touch…
I remember the day we broke up my sister texted him telling him she was disappointed with the way he treated me.

I broke up with him but only because he neglected me towards the end. Truth is he was just really busy with work and couldn’t make me his priority. I loved him very much but now I’m over him romantically I’m ready to be friends because I love having him in my life. We were great friends for years before we got in a relationship.

If anything it was me who loved him more than he loved me. So he should be fine with being friends right? It hurts that he doesn’t want to talk to me anymore…

What’s your opinion on this, guys? Why is he allowing what my sister said months ago to still bother him? What do I say to make him feel better about what my sister said? Or does it seem like he’s not interested a friendship with me and is he just using the sister thing as an excuse?