3°) Second conditional: "If I was your boyfriend, I'd never let you go" (Justin Bieber - Boyfriend)

This sentence it's an example of second conditional because use the simple past in the "if clause" and use would + base form of the verb in the "result clause". This conditional talk about unreal conditions and their results. In this example the "if clause" gives the unreal condition and the "result clause" gives the unreal result of that condition.