You need 30 love points when you get to the tribe restoration event. The initial flirtation dialog is a relevant point, where Usanna begins to study the protag and get to know him.
She is demanding, and if you don't have a "breeder" personality, this will lead to a drop in affection. That's part of Usanna's dynamic, who wants a strong, kind man who wants to have lots of kids with her and fight for her. She doesn't like pull outs, and she doesn't appreciate uncertainty.
If you're suggesting this is a big deal breaker, I can readjust that a little bit.