Don't be awkward. Just pretend they're not there and work like you used to. If they say hi, say hi back and start up a conversation if you'd like. They are you're ex for a reason, and it's because they're not the one for you. Be your usual amazing self and don't be caught up with worrying over that person.
Look forward not back.
You can just be friends with them^^
That's why it's not a good policy to date coworkers or Management or go into business with a boyfriend or husband re a company. I never mix business with pleasure. However, it does happen. Just be pleasant and start getting out with your friends socially and try to have some fun. Put work behind you and concentrate on your social life. Remember, work is work, and your personal life comes after working hours. Be pleasant, act as if nothing is wrong and get on with your life. Good luck