The slaves who fought for the British in the American Revolutionary War were freed, yes, but not the ones who fought for the patriots.
In fact, many southern slaveholders didn’t actively fight against the British for freedom because they were afraid that their slaves might get inspired to do the same thing.
British recruiters in Virginia augmented their fighting forces by making an offer that few slaves would want to refuse:
“Fight on our side, and we’ll free you after the war.” About 2,000 slaves took them up on it, including 22 who escaped from the Monticello estate of Thomas Jefferson.
After the war started winding down, most of the freed slaves found it wise to move to Canada; some joined an expedition to Africa to found the country of Sierra Leone.