Evan Rosier/OC Marauders Era fics
Now this is a character that has (understandably) almost no fics about him, so this should be a bit of a challenge. The romance doesn't have to be with an OC character.
I would highly recommend Come Away With Me by lucca4, which is Evan Rosier/Dorcas Meadowes and is simply excellent. Also Crushed by welshdevondragon is another gorgeous one, this time Evan/Marlene. The characterisation in both stories is fabulous, and the two stories I mentioned are some of those authors' best work in my opinion