I've got different agreements with different partners. I don't mention someone to Adam unless it's getting serious, and I tell Puck if I have met someone interesting enough to go on a date with.
It's a bit like a smorgasbord. I've told them l am dating. Relationship anarchy guy says it's none of his business what l do, polyguy says yes if l go out on date but doesn't need details. But l check in with both because it feels respectful.