Hi Tom, thanks for writing back to me today :). I am really sorry to hear you spoke your mind with your roommate but he didn't go for the cat or dog idea. I would suggest that you get more details from him about what his hesitations are. Is it because he is worried about the work? Or the mess? or is he scared of losing another companion? Letting him explain to you what his hesitations are might open up a conversation that will lead him to think a little more deeply about it rather than just turning you down. If it is fear of the mess or work, assure him that you are willing and able to take all responsibilities. perhaps even offer a 'deposit" in case there is damage or something. Also, perhaps pitching it more as something you guys can do as a team, including selecting a furry friend together, instead of trying it only from the angle of your wants and desires (which he seems hesitant to be wanting to meet), may make him more willing as he gets a stake in the idea, too.
The other thought I had is if you have a lease or written agreement? If so, does it say anything about pets? If this is a "real" property sharing situation which is under a contract as you pay rent, perhaps you will have some legal ground to stand on regarding your rights as someone paying for a service. I would hate to see you have to fight this from a legal battle, but it depends on how important it is to you and may at least give you leverage in an argument.
So basically, don't give up yet. Explore a little deeper with him and then try to make commitments or modifications based on his reasoning of why he is not allowing it. if it turns out he is just being cruel and rigid, then that leads you back to the place of either accepting and coping with this as best as you can while finding other ways to meet your needs for companionship, or considering it may be time to hunt for a new place to live where you won't be confined by someone else's rules.
I hope this helps some, Tom. You continue to have my support. i am not always at a computer but will always reply to you as soon as I am able.