Lyric discussion by zage513 

Cover art for Too Soon lyrics by Radio Dept., The

I think this song is commenting on fleeting love. The romantic interest eventually gets to know and 'figures out' the speaker, and decides the relationship isn't what they want, too soon for the speaker. Then the partner moves on to a new relationship likely to be just as brief. But rather than become bitter about this cycle, the speaker just savors love while he can.

@zage513 if it were about relating between only two people then the writer wouldn't use "us" and "we" when referring to themselves.