Mmmm i have a friend from work...?

I have this friend, who broke up with his grilfriend 1 month ago. At the begining he talked about how he felt and stuff, and i was there listening and giving some advice. He never listened so he continued calling and stocking his ex. Anyway, thing is he always have sth new to tell and sometimes im too busy. What he haves is an obsession to her. And im sick of it! He only talk about her, and tell the same story over and over. I have work to do and he wont let me. If we meet at work, he starts to talk about the same thing and im getting sick of it. What can I do?