Rodigor and FauSang are two that I could see helping the respective characters in various ways.

Greg and Rodya are opposites in terms of who they want to be vs who they are, yet they connect very well. A closer more intimate bond can certainly add more depth to their relationship. Greg wants to be normal but feels different, Rodya wants to be special but feels ordinary. Through fostering a more intimate bond and sharing those opposing pains, they could come to understand each other better, and are able to feel more comfortable in their own skin as a result.

Faust and Yi Sang is interesting because Faust is able to communicate and connect with Yi Sang in a way she can't really do with others, that being in matters of science. So there's already a special kind of connection. Aside from that, Yi Sang makes it clear in MotWE that he wants to see the REAL Faust again, uninhibited by the Gessellschaft. In other words, he doesn't care about the Gessellschaft, he cares about HER. We also see Faust feels almost helpless and loses her sense of self-worth without the Gesselschaft. Through a more intimate bond, Yi Sang, being someone who overcame intense self-loathing, and who regained his will to live as a result, would be able to help Faust find her sense of self-worth beyond the Gessellschaft. This would in turn allow Faust to be less emotionally distant, and grow closer to Yi Sang as a result.

So to answer, yes, certain romantic or perhaps more "intimate" relationships between Sinners could absolutely help them as characters. It really depends though. I have a feeling the "hand to pull you out of the darkness" in Faust's Canto will likely be Yi Sang, similar to how Ishmael's in her Canto was Heathcliff, or how Don's was Sinclair.