You will not really lose somebody by time gates, only by decisions made too early (i. e. stats aren't good enough yet to carry your decision - e. g. you need to get Sasha and Bree to a certain score in both love and submission before they will accept that you sleep with both of them, but it will only trigger after three times each; Hanna needs an idea or money to keep the gym, so you need the intellect or the money; worst case probably Cassidy where the storyline can change dramatically depending on how ready you are for the investigation)
Won't happen. (a) There is a Wiki now with all the relevant information; (b) the in-game hints are mostly pretty conclusive, with a bit of try and error you'll find out what to do.