Well, I can understand the frustration, but after all it is a game, very few AAA games tell you what the outcome of a decision will be. The same as in this game you just have to make the decision that makes the most sense considering the behavior of the characters.
But as I said, I understand the frustration. I would also be angry if the romance with Flora had been locked. Lucky for me Jacklyn is a no no. But if I remember correctly, in the quest about the date with Jacklyn, when Flora discovers that you are going out with her, there you get the option of romance with her or do you have to do the tree quest?
The thing is, to iterate: In order to make informed decisions, we need information, and it has to be consistent and reliable. There is a reason why Bioware tells you beforehand if you're making a Paragon or a Renegade choice: You may not know the exact outcome, but you can guess in which direction it goes in general, and you'll know in which way your alignment shifts. There is actually another part where Another Chance actually does this better: When you follow Lindsey's route, there is a juncture where you can either follow her, or break off to go chasing Maxine - and the game flat out tells you that you can do one or the other, but not both.
And yes, if I remember correctly, that is exactly my gripe with the Flora thing: The option to romance her appears gated behind information that you obtain through the Tiny Thirsty Tree quest ("Ask her what's really going on"), and there is no way of knowing that until you have to make that decision. I only found out by looking into the walkthrough.
I guess my point is: I wish I didn't need that walkthrough on my second monitor to confidently navigate the game, but could rely on the game to give me enough pertinent pointers to romance the girl I want to romance, especially since many of the quests are interlocking anyhow: You need to do certain ones to unlock others (like the beaver line to continue with Isabelle's quests) , so the game encourages you to advance quests in general - it's just that, as discussed, there is a order you "should" do them in if you don't want to miss out on quite a bit of stuff, and stumble into situations where the option you
want to take is greyed out because of that lack of information or stats.
It's not a biggy (despite me typing up a storm - I'm just overly verbose, I guess), it's more of a "I quite enjoy this game, but this is a recurring hurdle I keep having to step around - could we talk about how this could be done with less frustration?", I guess.