Have you ever had to choose between two partners?

I've been dating a guy for a little over a year now. We've been living together for a while, we've been committed to one another, but here lately, I feel like things have been off. Not wrong, necessarily, but like being together is just settling more than actually being happy.

Here enters my ex, the guy I was dating before my current boyfriend. He broke up with me for reasons beyond our control, but both of us still have feelings for each other, even after over a year. And with my feelings for my current boyfriend being called into question, I feel myself wanting to give things with my ex another go. I feel extremely lost and confused and no longer know what to think or how to feel. Could I get some feedback from you guys? What would you do?