DS is just 2 and talks and understands well. He is just noticing that some parents live together (ex and I split when he was 9 months) and will often ask "but where's his Daddy/Mummy?" when reading books or say "he wants his mummy/daddy".
I think it would be nice to get him a few alternative books that show parents living apart or something. Not necessarily a full blown explanation of divorce/family breakup, just a few alternative set ups, maybe?
We read books like the Gruffalo, Stick Man etc so anything around that level of text (or less is fine too) would be good.