Some companions really should hook up with each other if you don't initiate anything (Wyll and Karlach, Astarion and Minthara maybe?)
Astarion and Lae'zel,since they do start a thing during the party, if you don't romance any of them.
Tbh, I don't really care much about it anymore. The only companion, I have a problem with is Halsin, since his pickup lines are so incredibly creepy. And even after you said No, he tries it via your romance partner.
The rest is ok, imo. If you say no to Gale, you get a really nice friendship path.
