How Loki and Sigyn got married in the Marvel Comics.
Loki always observed and admired Sigyn from afar. He found her interesting in her debt rescheduling and beauty, wehlab gave her his most precious treasures as a present and she asked for her hand. Sigyn refuses this because she was already engaged and before Loki was out of the question for her.
Loki got angry about it and wanted to kill Sigyn for himself. Which is why he had Theoric killed and assumed his form. In this guise he married Sigyn and revealed himself to be me after the marriage. Odin and the others were very angry about it and the Allfather realized that he could not dissolve this marriage, even if he wanted to. Why he banished Loki, Sigyn accepted the marriage with tears and followed Loki into exile. Which is why Odin named Goddess of Fidelity.