I can give the perspective from a child who grew up from separated parents. When I used to come to see my father, I often felt unloved too. The reason is because everything was about my step mum's daughter, what she wanted to eat, what she wanted to do, what she wanted to talk about etc...
There was really nothing wrong with this because it was their normal dynamic when I wasn't there, but it meant that instead of feeling I was part of the family, I felt more like I was visiting someone's else family. For instance, they would spend a whole meal, talking about their previous' week-end visit to friends I'd never meant, bringing up conversations they had, plans they made, all things that meant nothing to me and made me feel excluded.
Or it was talk about DD's school and who went there, and what happened in the week. They never showed much interest in my school because they knew nobody going there, so it was usually a 5 seconds question about how was school and that was it.
There was also talks about future holidays they would go when I was away with my mum, everyone getting excited about it, looking at brochures.
None of this was malicious in any way, just that they didn't see the need to adjust their day to day life to when I was coming. As time went, I wanted to go and less and less. Things got better when I think my dad picked up on the dynamics and we started to do more things just him and I. My SM wasn't happy about it at all, so it affected my relationship with her, but at least I felt more integrated as I could have more of my father's attention.