I am torn between two lovers

Three months ago, I met this guy who became my best friend. He has been my greatest supporter in all ways! He's always there to support me in all things that I want to achieve in life. About a week ago, my ex-boyfriend came back from Europe and want to mend things between us. He wants us to be a couple again. I don't know what to do! This became more difficult when my best friend confessed his love toward me. I like him, especially that I'm starting to recognize a foreign feeling toward him. But I also want to fix everything with my ex. I am torn between two lovers now. What should I do?