Besides their love of animals, Halsin and Selunite SH actually have a lot in common:
1. Lives messed up a lot by Shar
2. Lost loved ones (parents/Thaniel) because of it and likely gained them back
3. Inner senses of turmoil they have to overcome on their journey (SH figuring out if she's really a Shrran after all, Halsin looking for a new sense of purpose after the curse)
4. Both actually enjoy being in their traveling party and having their companions close, and are among the most vocal about having missed the other companions
5. Both love extremely bad/corny/cheesy jokes and puns
6. Whether you like it not, both are poly, open sexually, and enjoy nontraditional arrangements
7. SH enjoys being taken care of in bed, while Halsin loves taking care of others
8. Clerics and Druids have a lot in common in terms of devotion to a deity
9. Both long for quiet lives post-canon and settle down in quiet, idyllic places close to nature
10. Halsin was too morally good to be a good leader of the more neutral Druids, while SH was too good to be a Sharran; both had their morals tested and concluded starting over was the better choice than compromising on said morals
That's not to say anyone has to ship them or anything, of course, but the claim that they have little in common is patently false. They have far more in common than even Halsin and Astarion or SH and Karlach.
