Lyric discussion by emoguy14 

Cover art for Sometimes lyrics by This Day & Age

I think there could be 2 meanings:

1) He's scared to tell her that he loves her, and he's scared that she already knows.

2) There's the line about "runs into the wrong arms" and "don't you think she'll find out" i just had a bad vibe off it, and i feel like its about them both cheating on each other.

Either way. Such a short simple song.