Stay strong. Anyone who refuses to share you had damn well better be able to give you a real relationship, not an endless litany of excuses and broken promises. Be prepared to walk away and not look back this time. People do it every day, you can do it too. What he's been asking of you is not ok.
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.