Losing one by one is a good Idea. It's less complicated and will probably be more fun.
Ehhhhhhhhhhh I meaaaaan kiiiiinda? 😅
The "death flags" are easy to spot. As in "girl tries to kiss you and you say no" styles of flags. The other part, having enough relationship points is another topic, but so far I've been very generous with them and there isn't stuff that's locked behind "need 100% of all points" or anything similar. As long as you start focusing that girl more and more in later updates, you're fine.