Try to keep your relationship issues separate from your career or education. Ideally, you have been doing this all along, but if not you will have to have a conversation about it. You don’t want fallout from a breakup to jeopardize your success at work or in school.  If seeing your ex makes you emotional, consider changing up your routine to avoid her. Take your breaks at different times, and plot out different courses to the copy machine. Imagine that your boss is watching you whenever you interact with your ex. This will add extra motivation to stay professional. If your ex breaks the “be professional at all times” pledge and starts discussing relationship issues with you, ask her to table the issue until later, or simply choose only to respond to professional communications. If this is absolutely impossible, make sure your discussion is taking place behind closed doors or via personal (not professional) phone or email.  You: Do you have that report ready to give to the boss? Her: I do. But before we talk about that, I really need to know when you're going to give me my stuff back. You: Can we talk about that later? Her: I really need it soon. You: OK. Please call me or email me after work so we can come up with a plan. If you’re worried about being caught alone with your ex while you’re microwaving your lunch, consider taking colleagues with you. Any awkwardness between the two of you will be less visible in a bigger group.

TL;DR in Vietnamese:
Cư xử một cách chuyên nghiệp mọi lúc mọi nơi. Trao đổi các vấn đề một cách kín đáo. Tìm người làm “bức bình phong”.