If they are really that close to a deal, then that source is no longer of any use to you, because what more info could your source possibly provide to enhance your investment? Not much.
So compromising him costs you only your integrity with that guy, and since you already revealed what that source told you without revealing the source himself, then it is arguable if your 'discretion' is really that good.
But who knows, on the other hand, you might gain some substantial political capital and member marks on this board by revealing your source, in exchange for losing your integrity with your source.
So weigh the pros and cons,
something for you to think about.
Krombacher