Thomas meant that the other person, to which the music refers to, knew something from someone (from some gossip - from some gossiper/blabber) and this hurt the relationship.
Or that the "singer" himself let slip something carelessly, or even some blabber himself let it slip in a careless way.
The thing is, the cat is out of the bag, certainly there´s no going back. And the singer then acknowledges that "Should've known better than to cheat a friend
And waste the chance that I've been given".
It´s no use to cry over spilled beans!
I like the romantic version best, with George Michael (the author/writer of the music himself), but then Seether have it in more Rock/pop version, not bad! Rockers deserve to listen good music as well, well done then!