This seems like a pretty straightforward problem that could happen in any relationship, mono or poly. You're in love with him. He's not in love with you. You can either choose to live with that or move on. With poly, you get the added option of living with it AND moving on... in other words, staying lovers but finding a second bf who WILL say I love you back.
Why not go that route?
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.