Dating Advice Needed!!?

So ive known this girl for about 5 years we hav been very close friends and just recently (around a month or so) ive been talking and spending more time with her bc im wanting to date her but i found out tht she is also talking to sum one else tht she nvr told me about. Wat should i do? Should i act like i dont kno? Do i confront her? plz help!