People aren't always who you think they are, and if in the end she couldn't be honest, well, that's a shame but it's a common enough story in both mono and poly relationships, and it doesn't mean that what you two had wasn't real. The only thing to do is soldier on, accept your sorrow, let your wife support you, and heal over time.
Was there ever any talk of opening things up so that she could openly see other people and not have to sneak around, or was that not an option?
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.