What is the best fix for this black triangle? I'm 22 year old. (photos)

wait for few more weeks , gum papilla will regrow. just maintain good oral hygiene. *if good amount of bone loss is there, in that case less chances of regrowth.

With the small amount of space and the excellent condition of your teeth, I would not recommend veneering your teeth.  By bonding a small amount of material the space could be closed.  My recommendation would be to see a periodontist to determine if there is an underlying gum problem that needs addressed.  There is also a treatment where dermal fillers can be injected into the gum to plump it back up and no treatment of the teeth would then be required.

It is not uncommon to get dark spaces between teeth, from gum recession, braces, Invisalign, etc.  Many solutions can be considered "aggressive" or time consuming/expensive.  Bioclear allows a conservative solution in a single visit and usually without removing any tooth structure.

I would wait longer and see if it starts growing back. If it was infected, it may fill back in because everything else is perfect for it to. If after several weeks it doesn't improve, visit a periodontist or gum specialist to see if something can be done. If there is nothing that can be done and it doesn't grow back, then i would look at bonding to eliminate the gap.Good luck...good oral hygiene is going to be your friend now