It sounds like you're falling into the "just because the relationship is ending means it was a failure" trap. I see poly as being true to who you are and open to opportunities, not as a mandatory "I must have relationships with other people" nor as a "superior way of having a relationship".
It's possible that you and your spouse are done, but it's also possible that you and your spouse are just entering a new relationship phase. Only you can answer that. But at least in the context of poly you have the freedom to answer that without the "I have to end this before trying anything else" catch 22...
33/bi, married to TheKnight (together 16+ years)
dating Sunshine and DinoActivist, TheKnight is dating
Sunshine. (Sunshine and DinoActivist are married.)
Other Dramatis Personae are detailed in my blog