Why is spending time with my ex seen as ‘wasted time’ I must move on from?

When I mention stuff with my ex, I say im doing what I want, when I want. Sometimes not everything goes the way I intended but that's life in general. I understand not interacting at all is like not putting myself in unnecessary situations. However we work together and live 10 mins away from each other.
To me it's more effort ducking and dodging instead of just chilling and talking. If im at his place, it's because I don't want to go home, I wanted to show him something, or I wanted to see what he wanted to show me. I don't go out of my way for him or spend time with him on my weekend
even if he's treating. The last time we went out together on an off day was not for him.
Id been wanting to go to this museum with his mom and I just invited him cause he was there. What's the wasted time on him? Wanting to know what he thinks? In my head, this is also considered wasted time too, getting opinions from strangers, but i do it because i like to hear other people's views. And move on? Where? Im already by myself. I use my weekend time for myself. Im not going on dating apps and I haven't been approached by someone im interested in dating. So I don't see how wasting time and "move on" correlate in this relationship. It sounds like y'all want me to use my energy to monitor his whereabouts so I can stay away from him because he's not going to stay away from me. The burden falls all on me.
Why is spending time with my ex seen as ‘wasted time’ I must move on from?
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