Ever notice how the slow drift often starts with the silence between texts getting longer? It's not the big blowout fights, it's the unspoken exhaustion. The inside jokes that don't land anymore, the weekend plans that default to 'maybe next week.' You stop sharing the little daily annoyances because it feels like burdening them. The distance grows from a lack of shared context, not malice. Like two plants in one pot that stopped intertwining.
I think a huge trigger is when life phases shift out of sync. One person gets consumed by a new career sprint while the other is looking for home and stability. You're suddenly living parallel lives under the same roof, watching different movies on the same couch. The emotional investment gets redirected elsewhere until there's nothing left to reinvest in the 'us' account. You become polite roommates who know each other's passwords but not each's current fears.
It's the death by a thousand paper cuts, really. Forgotten birthdays that used to be epic, conversations that never move past logistics. You stop being each other's first call for good or bad news.