Oof, okay, so this is a VERY specific pairing. I figure you're coming from the 'Vampire Academy'/'Bloodlines' fandom. I've been deep in there for a while, and honestly, Paul x Patryk is one of those 'what if' ships that has a tragically small but occasionally brilliant archive. You'll find the bulk on FanFiction.Net and AO3, but the tags can be a mess.
My absolute top recommendation has to be 'A Different Kind of Moroi'. It's a complete, long-form AU where Paul is raised with the Strigoi instead, and his eventual collision with Patryk is a slow-burn masterclass in enemies-to-reluctant allies-to something much more. The author nails their voices—Paul's quiet intensity and Patryk's weary, duty-bound stoicism—and the world-building feels like it could be a Richelle Mead side novel. The tension is palpable without being melodramatic.
For something shorter but emotionally devastating, 'Cinders and Smoke' on AO3 is a standout oneshot set after the final battle. It's all about shared trauma and silent understanding, with Patryk helping Paul cope with the physical and psychic scars. The writing is so atmospheric it gave me chills. Honestly, without fics like these, I probably wouldn't ship them half as hard. They fill in the gaps the books left wide open.