You could always bring up the idea of polyamory to your husband. If everyone can agree on it, you wouldn't have to leave anyone. It would be a difficult conversation, of course, with no way to know how it'll end up, but... at least it's a chance, and some spouses really do come around and get it and accept it. www.morethantwo.com
is a great website for helping people unfamiliar with poly begin to wrap their heads around what it's all about.
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.