Unfaithful?

The question is, can we put faith in someone who is unfaithful? This question/statement has been bouncing around between the walls of my brain since this mornings church service. What exactly does that mean? It has stopped me in my tracks.

For instance, I have a new found friend. I'll call him Jerry for alias purposes. Jerry seems to be a nice guy, a sweet guy, a polite guy, even a handsome guy, BUT whenever he says something, I don't know if I should put total faith in what he says. His actions never seem to follow his words, even though he seems most sincere. Does that mean he's 'unfaithful' and if it does, should I not be putting faith in him? Faith that he's going to follow through with his word or faith that he's actually going to do what he said he would....