You need to break off contact with her 100%...which seems like it might be next to impossible with you working in the same office. You might think about finding another job...sounds drastic but do you want to save your marriage? It will take time...do some reading about what causes affairs...figure out what is missing in your relationship that caused you to do what you did. Recommit to your wife!!!
You might want to read over these articles on infidelity:
Infidelity
