Do you have to have a different Web site for each affiliate relationship?
There was a time in the early days of affiliate marketing when some affiliate programs demanded exclusivity if you wanted to be in their affiliate program.
You had to exclude all other competing companies in their category if you wanted to run their banners.
Over times, the affiliates realized the real estate on their site was a bargaining chip and they rejected the calls for exclusivity. In some cases, affiliates would accept the requirement on the condition that they were paid some extra points for the right to be exclusive.
They were going to promote who they wanted where they wanted. And if merchants didn’t like it, they faced a thinning herd of affiliates willing to play that game.
The concept of exclusivity was pretty much gone until Google AdSense came onto the scene. Their terms of service dictate that an affiliate cannot run competing ads or services on a page with AdSense ads.
So anyway, in general you do not need a different site for each affiliate relationship. Be sure to read the affiliate agreements before promoting any affiliate program to be sure you are compliant with their rules.