Remember, don't read into things, dont let your head wonder, try to be yourself, dont talk about the ex unless asked, enjoy a walk in the park, be a gentleman, and most of all don't be affraid of any outcome. Don't be affraid of getting hurt, don't be affraid of hurting her.
Heck even if the two of you don't have chemistry, as long as it was a good time as well as a learning experience, you can walk away from it knowing that you've become a stronger and better person and discovered more about yourself and how to interact with others. Plus you got to try something new
lets not forget the cardinal rule that we all learned from our divorce experience. Its better to be painfully honest than to be ignorantly blissfull.