I think it depends what you mean by "first". What does that mean to you, @Blashed ?
The hierarchy I think is reasonable is:
Children's needs (because they need help to achieve them); then
Adult's needs; then
Everyone's wants (roughly equally, given you can't do everything).
If you mean how much someone loves someone else - I don't think it's relevant as there's not a finite quantity of love, nor is love for a partner the same as for children.
I do always wonder whether there is a difference in views between parents who are still together, & so their relationship predates the kids, and parents who are with other partners who came after the kids. I think there is a difference, though I'm not sure theoretically it's reasonable.
However, you raise your kids to grow up and forge their own (independent, adult) lives, whereas I intend for my partner to be a lifetime companion, so I think it changes over time.
Adult children's needs no longer come first by default, and as they grow, there's a gradual transition as they are taking more responsibility for themselves, which starts when they are still children, it isn't a sudden step change at 16 or 18...
This is a topic that pretty much always gets very black and white responses on MN though, and anyone suggesting that children aren't the absolute priority for all time usually gets short shrift.
Ultimately - everyone's entitled to their own relationship boundaries, and if he can't offer what you need, you either accept what he offers or find someone who offers what you need - but being upset about something he's unlikely to change might make you quite unhappy and resentful over time.