I recall that Larian stated that they will fix romances and what not down the line in a future patch so players can avoid unwanted romantic interactions with companions as that was the number one complaint they got for the game. To be fair to Larian they stated that this was the first game of theirs that they implemented romances for and with the romances they mostly relied on player feedback during Early Access. One must remember the type of "fans" that infest D&D nowadays. Porn sick troons. It has gotten to the point that even our Feeder Lord has noticed a correlation between troonism and D&D. My guess is that troons would have thrown a fit if some companions were locked out of romances due to sexual preference. It is obvious that Gale and Minthara are coded as straight but we can't have companions have their own sexual preference as Jim Sterling and other troons would have gotten ass blasted and talked about how transphobic the game is due to companions not wanting to bone their dick girl character. A reminder that these people are a pestilence to every hobby they invade.
I think the only thing that bothered me about BG3 was the fact that all the companions, with the exception of Minsc and Jaheira is that all the companions clearly were written with certain orientations in mind before it was changed, likely at the last minute. I'm generally not a fan of "Protagonist-Sexual" characters, that's one of the reasons why I disliked Dragon Age 2 and the "romances" in Fallout 4 annoy me.
Straight Companions:
Lae'zel: - I don't know why but she doesn't seem to be the kind of person who would be into chicks
Gale: - There is no way that this guy is gay.
Minthara: - She had a cut storyline where she would get pregnant from a male Tav/Durge
Jaehira: - She is canonically straight.
Bisexual Companions:
Wyll: - This was a tough one, because he's clearly got a thing for Karlach, but that little dance he does in Act 2 put him firmly in the bisexual camp, with his obvious feelings for Karlach and how he hits on Lae'zel and Shadowheart being the ONLY thing that has him not tossed into the gay pile.
Karlach: - Despite clearly having feelings for Wyll (You can't convince me that an unromanced Wyll and Karlach aren't in their own relationship) Karlach really comes off as a bisexual chick. Also she either pegs a male Tav or rides him Amazon style.
Gay Companions:
Halsin: - The dude is literally the definition of a homosexual bear and he also TURNS INTO a bear, with that being his preferred beast form. Also he's an elf and that makes him pretty gay
Astarion: - He's a twink, he has obviously gay mannerisms and ways of talking, he's a vampire, and oh yeah, he's got that little scene with Sebastian, the dude he seduced and clearly still has feelings for. Oh yeah, and he's an elf, so that makes him gay.
Shadowheart: - I'm sure a case could be made for Shadowheart to be bisexual, but she's pretty obviously gay, I think, with her comments about Karlach and how she shuts down Wyll's flirting really, really hard. She reminds me of a couple 'lipstick lesbians' I know IRL. Also she's 50% elf so that makes her pretty gay
Gortash (For the one quest you get him lmao): - Dude is a FFXIV protagonist who experienced twinkdeath. Have you seen his fashion choices? GAY
Alfira (For the single cutscene lmfao): - Yeah she's in a gay relationship with another Tiefling.
??? Companions:
Minsc: - He has no time for romance. He serves a greater power: JUSTICE!
Dream Guide / The Emperor / Balduran; - He's a psychopathic squid monster gaslighting you and if you call him out on his shit he drops the act and strops trying to manipulate you via sexual attraction. Before that though he was pretty clearly gay since he was in a relationship with a male dragon.