If you feel you both still have feelings for each other then you are going to have to get some kind of closure for those feelings but meeting might not be the best idea for that because if you see each other again it may bring all of those feelings to the surface, if you are sure that you can meet without it going any further than old friends having lunch or talking but still I wouldn't jeopardize his marriage or your relationship. If you do this you have to do it when you both are free and single. I can understand your feelings come flooding back into your heart for him but the simple truth is that he is married. If you feel you have to do this to see if there is feelings there or if things have changed then you have to make the final decision but if you decide to do this then take into consideration if you would want your husband to meet an old flame without you around. Is your gut telling you to meet or is your heart telling you to? There is a difference because many times out heart can lead us to do things our minds wouldn't allow us to do. If you think meet will be okay and the two of you can contain your feelings then I would meet him in a public place and not stay at the same hotel and not be alone it's important to do this the right so that you both can have a clear conscience and won't be hurting anyone.
It's never a good idea to live with regrets especially when you have had other disappointments but it's also important not to have to regret doing something that you knew was wrong so if you feel you won't be intimate then surprising him on his birthday is XXXXX if you are meeting as friends, bring a gift but make sure you wouldn't do anything that you couldn't do if his wife were with him. There is nothing wrong with meeting a good old friend before they leave for Afghanistan. Make boundaries and don't cross them and then make sure before you leave you are clear on what this relationship is going to be and if you want to find closure do that but if there are stronger feelings there you are going to have to tell him that you won't do anything until he is single and free to do so. Always start on the right foot in a relationship so that Karma doesn't come and bite you.