Desc: Works like the Bouquet, but you have to make it. Two fabric and any 'Gems' (Except Prismatic shard because, come on, that'd be ridiculous) . Give it to the 'single' NPC that you have with 8 hearts and it unlocks the ability to have 10 hearts. It would be unlockable as soon as you hit 8 hearts like the bouquet did. Name change under the NPC's name to be "Friend" instead of "Single". Catch being, it blocks the 10 heart cutscene for less awkwardness. For those who want to play the game with only one spouse and a lot of friends and not one spouse and the rest of the eligible community being their various boyfriends and girlfriends. To be fair, I have no idea if this is doable: New Crafting item, New Sprite (The bracelet in the crafting window), New dialogue (Somewhat), Blocking a cutscene from happening, unlocking 10 hearts for potential spouse NPC's. But just tossing this idea out in potential mods or game additions.
I... Third it? Whatever. Anyways, this is actually something I've also been thinking about for a while. My theory is that it would come before the 8 heart event, so that you don't have to see romantic stuff like when Abigail's Ouija board tell you she loves you. That was so sad... I felt so bad. You could have a similar event and just make it send a "I'm so glad we're BFFs" message instead of a romantic one.
This is an amazing idea, you could always try pitching it to concernedape! He might love the idea and implement in a future update?