I'm looking for a story Sirius/Oc story where he falls in love with a girl who ends up being a spying on Voldemort during the Marauder Era. She's best friends with Lily and Alice and the Marauders. She was close to Regulus and tried to get him to leave the Death Eaters but one night Sirius saw them together. She had a daughter w/ Sirius in a sequel.