There was a period in history where there was co-existance between Nedes and Mer, during this time some crossbreeding went on and created Half-elves, which in time, due to half elves breeding with Nedes evolved into what wee see as Bretons. Several events split the Mer into several different races (four of which, Altmer, Bosmer, Dunmer and Orcs) and men into two different races (Nords and Imperials).
Redguards, although offiicially classed as a Man race, were from a different part of Nirn and have nothing to do with Nede's.
Am I right, just want to clear this up?
Nords view Bretons as weak, effeminate and devious, not to be trusted.
For the most part you're right. Redguard aren't completely removed from the other races of man though. All Mer(including Khajiit, who were turned catlike by Azura) descended from Old Ehlnofey and all men(Nord,Imperial,Redguard, and partially Breton) descended from the Wandering Ehlnofey. Argonians were created by the Hist, sentient trees that are the only lifeforms that didn't descend from the Ehlnofey.
EDIT: Although its not totally clear how the Bretons became like they are now. Usually when races mix the offspring takes the mothers race, but it can be assumed that if mixing continues for long enough, like with the Bretons, that the line become more blurred, and a true mix occurs.