I still pull out my old CD booklet sometimes when I want the "real" words — so my first tip is the one I trust most: check any official physical release of 'The Black Parade' (CD/vinyl) for the printed lyrics to 'I Don't Love You'. Those liner notes are as official as it gets, and I love the tactile feeling of flipping through them while the record spins.
If you don't have the physical copy, look for the band's official channels: the My Chemical Romance website (if still hosting archives) or the band's official YouTube channel/record label uploads. An official lyric video or an official upload from the label (Reprise/Warner) will usually have accurate lyrics in the description or embedded as subtitles. Streaming platforms like Apple Music and Amazon Music often display lyrics pulled from licensed sources, and Spotify shows synced lyrics too — those are generally reliable when they come from verified sources like Musixmatch's verified artist pages.
If you need printed, licensed lyrics for performance or study, buy the official sheet music or songbook (publishers like Hal Leonard often release songbooks with verified lyrics). For copyright-cleared uses, the music publisher or licensing agency that owns the song’s rights is the place to contact. A lot of fan sites and Genius pages have great annotations, but if “official” is your priority, stick to the band/label releases, the physical booklet, verified streaming lyrics, or published sheet music. Personally, I usually cross-check two of those sources when I’m learning a song for a cover — gives me peace of mind and saves me from singing the wrong line mid-bridge.