After few hours i finally understand how it works, read carefully.

on the first day if there is no need then it is better not to touch them at all, otherwise the relationship will drop to 0, it is better to give them time and contact only when necessary (for example food or cleanliness, or socialization). after that again you can not communicate with them for several days (the relationship itself will slowly rise), but you should not forget about them completely, but I think this is obvious. well, I hope you understand how it works, if it is not clear then write

I normally just edge them with no penetration, and not letting them cum. Every time they lose the Horny status, bring it back up to just before they blow again. Just keep doing that until they accept to join you for free. Then give it to them. I also found that if you just make them cum repeatedly their relationship status goes up too, but I didn't think that was as fun. It does take less time though

Why ts works like that, this game is cursed