May I reuse my own figure without coauthor's permission?
You -- and your co-author -- have, most likely, assigned your copyright in the paper to the publisher. 

Without knowing all the details of your copyright agreement, your copyright agreement seems to allow you, and your co-author, the right to re-use the work, and that right applies to each of you separately. The right to re-use the work requires you to reference the original paper and all its authors. 

I see no reason why you shouldn't use the figure, even without the permission of your co-author, as your copyright agreement with the original journal appears to allow this. I see no ethical argument against re-using the figure, either. 

P.S. I have a qualification in intellectual property law, but I am not a lawyer.