I'm just going to take a moment to take issue with one word here -- trapped, from your subject line.
You're not trapped. You can leave any time you want. I know it may not feel that way, and I know you can't imagine loving someone else, but all that comes back to being young and being scared. You CAN say "I care for you, but this isn't right for me." You CAN move on and love and be loved again. I hope you can come to believe that.
I'm not saying that staying or leaving is right in this situation per se, but I think you'll be able to make a better decision one way or the other if you can work on learning and believing that you truly are free.
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.