Maybe you should preemptively come out to your parents, just in case? It's something you probably would have wanted to do eventually anyway, if things got more serious. Maybe if both you and your husband were there, and spoke equally during the coming out, your mom would be less likely to freak out?
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.