It depends on the context but can mean frustration or something sad or angry or scared it can express many different types of emotions.
Her: I lost my airpods today :(
me: reee I am so sorry :c
or
Your GF: I cheated on you....
You: REEEEEEEEE!!!!!! HOW DARE U!!!!!!! >:C
or even
GF: I bought you a brand new Playstation for your birthday!! Happy Birthday!!! <3
You: REEEEEEEE I LOVE U SO MUCH <3 :)
or even
Damn this box is heavy REEEEE
or
*steps on a lego* REEEEEEE OW THAT HURTS!!! >;c
last example
BOO!!
REEEEE!!!! Don't scare me like that D;
HAHAHAH :D
The most tasteless member of Jack Nation
Person 1: Omg my friend is such a ree!
Person 2: Really?! Reemove them from all your GCs!
When you and your crackhead brother are speaking in meme
"DISGUSTANG!" "REE!"
A beautiful individual who just has a charm that woman love even tho he’s is a piece of shit also is a freaky horny bastard
A kid that is a bot at fortnite and is a cringy Tic-Tok kid. He also sells ree burgers on the black market and adds extra ree sauce