Here is some background information on the song from the Drunk Songfacts: Sheeran's fourth single from his debut album + finds him singing about someone whose relationship ended because of his own inability to change. The protagonist feels sorry for himself and the only way he can handle the pain is by drowning his sorrows in drink.
Sheeran sings of getting drunk on several other + tracks. He recalls getting…
I wanna be drunk when I wake up
On the right side of the wrong bed
And every excuse I made up
Tell you the truth I hate