Mum! Always mum (although I think I'll get called 'mama' when I have a baby.
I'm so relieved that most people in my life are ok with it. I think it's because we'd lived together 18+months prior to starting a relationship so it seemed like a natural progression even to people who are firmly mono. Plus most of our mummy friends art totally jealous of my bestie for having me, with or without sex. lol.
And Ironically when coming out to my parents, I learnt that open/poly relationships run in my family