Help me complete this phrase?

When someone dies, what's that expression that means that you don't want to do something because it would taint/dishonor their memory? Like, for instance, if a girl's fiancee just ped away, and another man asks her on a date, what would she say? I was thinking along the lines of "No, it would be unfaithful to his memory.", but that's not quite it. Can someone come up with the phrase????