Julie x Lily Greyrat will be a thing. Yes you read that right.

The main reason: In Japanese, the word for a (white) lily is yuri. Yes, the exact same word used to refer to girl's love. Rudeus and Roxy basically named her Lesbian. On top of that, here is a excerpt from LN18 where Julie talks about her mother Lilitella's ornaments:

What stood out most in Julie’s memories were her mother’s ornaments, carved out of wood. She could whittle a block of wood into the most beautiful lily. Julie couldn’t remember what her mother had eventually put those lilies on, but she vividly remembered the flowers themselves. With those memories as a guide, she carved lilies into her own box. Seeing it gradually approach completion made each day more enjoyable than the last.

Taken symbolically this can mean Julie would potentially be fond of Lily AND yuri.

Every child of Rudeus that got married so far has picked one of the kids of one of Rudeus' acquaintances as their SO. (Lucy-Clive , Ars-Aisha, Chris-Edward). We haven't any indication about Sieg and Lara's partners, but assuming that there will be a sequel/story set in the same universe, Lara will certainly play a big role as the savior and would likely pick a guy connected to that whole situation (ex: Shinohara Akito, Kalman III, the original savior, someone else), which might possibly be interpreted as picking someone associated with either Nanahoshi or Orsted. It's hard to say about Sieg though (maybe Pax Jr. counts), but I think he will also play an important role in the sequel, though not as the main character, so there is more opportunities for that to happen. I also have a theory that Laplace will be Sieg's son/grandson, so maybe that ties in somehow.

Additionally, Lily goes to work at the Zanoba store, so perhaps her partner would be Zanoba's "kid" (Julie). Considering their extended lifespans and talents, I imagine that Lily and Julie would become the head honchos of the business eventually, meaning they would be in close contact with each other (perhaps with Julie managing the figurine/arts side and Lily on the magical implements side).

In Jobless Oblige, we also see Lily dodging marriage proposals for no apparent reason, suggesting she isn't very interested in men... And Julie wouldn't be the first gay dwarf we've seen either.