To get the engagement ring, which can be given to marry one of the demons, you must receive the silver ring in 1-1, basically the room next to yours where you find the blonde girl and the diamond, which is found in Arachne's cave, which is reached through a ledge near the end of the spider familiar section.
i'm all out of rocks and gems where can i farm like demon sake or something?
i need more friendship to get hell break.
You can farm gems and stuff using the bronze boxes, which are usually the first reward you receive. Here's a lost of useful drops.
Here's a tip however. You know how you can only handle three drains with a demon in My Room and then wait for it to cool down? Well using tea resets that and allows you to go at it again.
It's important you utilize this and press down SHIFT and CTRL once to enable the faster skip added by the translators to speed up the scenes (Although doing it during story will break things, so only use it in My Room).
Stay safe and hope it helped.
Till next time.