In order for Tough Love to be activated, one must enter a romantic relationship with the Iron Bull. Additionally, the Inquisitor must approach the Iron Bull about the status of their relationship and prompt the dialogue option discussing how serious their relationship is. The Iron Bull will indicate that under the Qun, most never enter serious relationships but when two Qunari (or people) choose to commit, each wears half a dragon's tooth.
Once the Inquisitors has prompted this dialogue, the quest will be active. The Inquisitor must kill a dragon and craft the necklace using the Requisition table either in Skyhold or any camp site.
Upon delivering the necklace, there will be a comical cut scene between the Inquisitor and Iron Bull in the nude, where the two are interrupted by Cullen, Josephine and Cassandra. Following this, the Inquisitor will be prompted to pass over the necklace and enter a relationship with the Iron Bull.