I believe there's some confusion here. As far as I know from 'The Boys' series, Homelander never killed Black Noir. In fact, in the comics version, it's quite a twist because Black Noir turns out to be a clone of Homelander, created as a failsafe should Homelander go rogue.
But in the TV series, this storyline hasn't unfolded yet. If you're referencing to a specific scene or episode, could you please clarify it further? Or perhaps you're mixing characters or series up, it happens to the best of us!