I think the deepest kind of pain ever had in my life is relational pain. There's a lot of hurt that we all experience in life. But there's something about relational pain that can hurt so deeply that it's really hard to let go.
Maybe you are in a relationship that is falling apart right now. And in that process, someone has hurt you in such a way that it feels like it would be impossible to ever rebound from that situation.
Maybe you were betrayed (a friend repeated a secret), abandoned (a spouse/parent left you), or trust was broken (there was an affair).