When me and DH first met he has a set up with his ex (who was single at the time and on a lower wage) where he'd contribute towards her going on holiday every year with their children. There was no maintenance paid as they've always done 50:50 but he used to pay towards her holidays.
We've now been together for nearly 6 years and this is still ongoing. Its not just expected and imo should stop. DH has made suggestions before in the past that it stops but it's always met with complaints and kick offs and to keep the peace he ends up carrying on for another year.
The ex is now with someone else herself and has been for a couple of years, we also have joint DC to think about too, a bigger home than before etc etc.. all meaning spare money isn't as easily found as it was before. Its not that it's not affordable but more that the money could be used for more important things for OUR family and in my opinion she should now be supporting her own holidays with her own job and partner if she wants to go away, I've always thought the arrangement was odd and a bit cheeky but I lived with it at first. Now I just think it's ridiculous.
Aibu to say to DH this really needs to stop now? He'll agree with me as he's wanted to stop for a while but I know she'll likely moan she can't go away with the children otherwise so it's just about getting him to keep saying no despite the fall out.