Green’s Dictionary of Slang

(US black gang) one’s intimate friend.

1964		R. Abrahams Deep Down In The Jungle 268: Tight – Good friends.
1980		E. Folb Runnin’ Down Some Lines 35: Teenage folklore has the terms tight and squeeze deriving from being in a tight situation – a tight squeeze – and having someone there with you; or, you are squeezed tight together in friendship like peas in a pod.
1991		L. Bing Do or Die (1992) 47: Crazy Dee was known to be Monster Kody’s ‘tight,’ his ‘road dog.’.