I guess what I'm trying to say is I need the deep end
He longs to be in “the deep end” of a relationship, and craves all of the problems and joys that it brings.
He’s trying to calm down and put it in a more laid back way to save face saying he just needs to know and have it all or none instead of being so open like he just was.
The “deep end” could be Alex’s allegory for what lies below a woman’s waistline. That is why he keeps imagining meetings and wishing away entire lifetimes and it’s unfair that he isn’t misbehaving with her.
To help improve the meaning of these lyrics, visit "R U Mine?" by Arctic Monkeys Lyrics and leave a comment on the lyrics box