It is a tricky situation and it becomes very difficult to work in a same office where ex also works or have joins. So what should be done especially when you have to see each other at work and in worst case what if you have to work with them on the same project or you in same department? An office breakup can affect you not just personally but professionally also as it may hamper you productivity and sometimes can also be demotivating.
Here are some tips which could be useful for you if you are in the same situation and will help you to deal with your ex when she joins your office and becomes a co-worker.
First thing you should always remember is that you are not together anymore and keep reminding this thought to yourself and be professional as by bringing personal problems at work will only increase your problems. Just keep trying to be as professional as you can no matter how difficult as it may seem, treat your ex as just another employee of the company.
Think clearly about your relationship status with your ex as if you have already decided not to be in a relationship again then it is always better to cut them out and do not enter in their life again on personal level.
If you still have not been able to come out of the break up then never talk about this with your ex again as it will only disturb both of you.
Never talk about your ex with anyone in office coworker, as they are going to find about it sooner or later. So the golden rule is that never gossip about your relationship with anyone or it might create problems at the workplace. Just let break up things between you two.
If you find that you ex is going to move on then it is always better for you also to forget about your past and it is time for you also to move on and ignore thinking about your ex. Accept the reality as this is the best way to go about it and do not react.
If your ex is ignoring you at the workplace then you should also follow the same principle and behave as though nothing has happened and simply mind your own business.