Question about business arrangements

Hi! I'm new to this board. I found your board by doing a simple google search. Honest!

I own a website. It gets a lot of traffic and other companies recognize this. I have an arrangement with one "Company A" where I will promote their site for shopping needs, while they will promote my site as their exclusive message board. Good arrangement. Good $$$.

However, another company has entered the picture. Let's call this company "Company B". Company B wanted me to post a link to their site right next to Company A's link. At first, I posted a link to their site, but Company A complained to me about the EXCLUSIVITY of our deal. So, I complied and deleted the reference to Company B.

I explained this to Company B. Their only response was "What suggestion do you have to make this happen?" which indicates to me that they still want to be on my site and are open to any ideas for that to happen.

What can I do? What should I do? Any ideas?
Thanks!

p.s. I realize one possible answer is "What part of EXCLUSIVITY don't you understand?"