I might be pregnant from my brothers best bud and my brother knos nothing...what should i do!???

You don't need to tell him anything until you know for sure your pregnant. If you are, he is your brother and he loves you i'm sure he will understand that you and his friend are in love and he will be happy for both of you. If not give him time i'm sure he'll come around. He may feel hurt that the 2 of you did this behind his back. If your not pregnant you need to tell him about your relationship it's not fair to him that the 2 people that he cares about most are doing things behind his back.