In any dating endeavor there is a 50% chance of success or that of faelure.
If it works out, know that you are lucky enough to date someone who is socially adept and usually will be a fun person to hang out with. They keep odd hours and tend to drink more than the average person, but relax, to those in the trade it can all be chalked up to research.
So if it doesn't work out here are some tips:
Don't go to their bar by yourself or on a date on the nights they are working. It shows either you are lonely or that you are trying to show off your new person. If you happen to be a part of a group that wants to visit the establishment don't feel awkward or the need to point out the fact that you and the bartender used to be an item. The bartender should be happy to have a group of people drinking and wont think you are sitting alone at home or you have a lack of friends.
If you happen to run into your ex-bartender at a different establishment there are different rules to adhere to, for both the bartender and the ex.
If the bartender is there on a date and the ex comes in by themselves, the bartender should realize that their ex was just going to have a drink or meet up with a co-worker or friend and since the bartenders plans are already set they have control over changing the situation and relocating.
If the ex comes in with a date, just play it cool. You are both doing your own thing now and feel happy for the other one. Just play awkward until the other one is adult enough to go and say hello.
If the ex comes in with a group then access the group to see if you know anyone, or if its seems like a group that you approve of, then use your ex as a lead into making a few new customers.