The speaker looks back on a relationship and admits that their actions may have caused their partner pain. They also recognize that this person stayed close during difficult times. The song moves from regret and memories of wanting to leave toward a promise of loyalty and an emphatic declaration of love.
“Cried a river of tears” is an exaggeration meaning the partner was very upset, not that they literally cried a river. “When the sun goes down” and “nights grow colder” suggest lonely or difficult moments; the speaker promises to be there through them. “Looking over your shoulder” means watching out for someone or offering support, rather than simply standing behind them.
The repeated idea that deeper love brings stronger emotion and devotion presents love as something that grows with closeness. The speaker’s earlier wish to “break free” sits beside the later promise never to let the partner go, suggesting a change of heart. Still, “I don’t mind what you’re doing to me” could sound like complete acceptance, or perhaps a willingness to endure difficulty for the relationship; the lyrics do not explain exactly what is happening between them.