They have three browser tabs open comparing flights to two different countries, and somehow this is turning into a debate about whether the trip needs a plan at all. Libra wants an itinerary, or at least a shared spreadsheet with restaurant options color coded by neighborhood. Sagittarius wants to land somewhere and figure it out, maybe not even unpack the suitcase properly, just chase whatever looks interesting that day. Neither of them is wrong, and neither is really annoyed either, which tells you something about why this pairing tends to work.
Libra is air, Sagittarius is fire, and that combination usually feeds itself rather than draining anyone. Air gives fire room to spread, fire keeps air from getting stuck admiring its own reflection, and together they end up talking for hours about books, politics, people they met once and never forgot. Libra brings the social polish, Sagittarius brings the bluntness, and somehow the friend group ends up more entertained than offended.
The friction shows up in modality. Libra is cardinal and likes to initiate, shape, negotiate the terms of things. Sagittarius is mutable and resists being shaped by anyone, including someone it's genuinely wild about. Libra will try to set a direction for the relationship the way it sets a table, thoughtfully, with everyone's comfort in mind. Sagittarius will feel the walls going up before Libra even notices it built any.
Venus and Jupiter get along fine though, both expansive, both fond of pleasure and generosity. What keeps this alive is Libra learning that Sagittarius needs air in its lungs, not a leash, and Sagittarius remembering that Libra's need for harmony isn't the same as control. Give each other room to negotiate the itinerary instead of one person surrendering it, and this pairing rarely runs out of things to say to each other.