Hi! The game comes with a full PDF guide within the folder :) Unfortunately during the making of this game I didn't know how to create a system to check affection unless someone is following it, if his affection is at its highest and he has confessed you can propose with a special ring (shown in the guide) then marry him when you have the wedding dress.
In regard to the basement if I remember right (haven't worked on the game since its release) you need to advance through the story before you can enter.
I'm glad you are finding it fun, please do message again if you are unsure of anything else!