You say your sadness has been based on missing him, not on jealousy. That's a really good sign! You may not really know until you try it, though. Maybe keep things with polyman somewhat casual for a while so you can get used to the idea.
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.