Sigyn is the goddess of fidelity, the only one of several deities with love as part of their purview in the Norse pantheon who represented the concept of spousal loyalty. She was evidently of the Aesir tribe, but her parentage isn't mentioned in the surviving myths. In fact, scant information about Sigyn outside of confirming her status as a goddess is available in the remaining recorded myths, save for her marriage to Loki, the god of mischief, and her great love and loyalty for the trouble-making Trickster god being demonstrated by her diligently holding a bowl over the dripping corrosive venom from the mouth of a serpent evidently native to Jotunheim, the realm of the giants, as the horrid poison poured down on the bound and trapped Loki--who was consigned to this extremely painful punishment and confinement by his fellow deities for initiating the death of Balder, the beloved god of light.
Sigyn is one of the deities who I have established a fairly strong spiritual bond with, as I have called upon her aid in the past. She is a kind goddess who is greatly loyal to all those she loves, including not only her errant (and not exactly faithful) husband Loki, but also all mortals who follow the Norse path. She can be called upon not only to acquire love for oneself, but specifically a lover who will remain loyal to the spellcaster, or more specifically, a lover who has a natural affinity for a monoamory, or in other cases simply a strong sense of loyalty in general. Though I do not presume to argue that monoamory is something that is for everyone--either mortal or deity--some people do hold it in high esteem and consider it highly important to their emotional needs, and in this case Sigyn is a good choice of love deity to call upon to bring a lover with naturally monamorous inclinations and a strong sense of loyalty to those she/he loves into your life.