yeah, the Antilycan just makes it so they can remain in control at all times even when transformed. it's not a true cure.
it doesn't do anything bad CURRENTLY, but it WILL someday in the future as it's a red option and those always have a consequence later on.
and for who can you date the answer is literally any and every character you meet that has a relation log. not reputation, relation. if you want to know if you'll eventually be able to romance a character, just check that. if they have one, they can eventually be someone you'll date. listing them all would take a minute and I am entirely sure I wouldn't be able to remember them all off hand lol.
for the love triangle thing, it might happen more often later with other character's, but currently it's just a special event between us, Bernard and Logan where we have to choose which of the 2 we wanna go on a date with. you can still do the event with the other person even after you've done the first date with the first person.
also there is no limit to how many people you can romance. I've gotten a LOT of hearts lol, maybe someday it'll bite me in the ass, but at the same time it prolly won't because one of the main appeals of this is the sex stuff, and limiting your options in a game like this would be a bad move.