Co-parenting and preferences

I’m not sure what my point is, I think I just need some guidance from past experience and some reassurance.

I have been separated from my ex for 6 years, we have a 7 year old son together. I was the primary parent until a year ago when we went 50/50 split. It’s always been amicably handled between us with no legal agreements in place.

I’m struggling with my son starting to prefer my ex, despite the fact that he’s had less input, handled less of the big/difficult parts of parenting, and doesn’t make choices based on what’s best for our child. He’s a good dad, just a bit clueless.

I’ve worked hard as a single mum to provide for him and set us up, I’m raising him to be as emotionally aware as I can and to equip him with social and life skills but it hurts watching my ex do the bare minimum and be favoured. I know it’s a natural part of growing up, but I’m struggling to adjust, maybe a bit bitter about it. My son obviously is not privy to these feelings and I never stop communication/visitation between them.

I’m worried about our relationship as he gets older. Is anyone on the other side and can offer advice?