Best friend is seeing my ex

So me and my ex split up a week ago. Am still love with him and been in bits crying over him, not we was together just under ayear. I’ve found out tonight that him and my best friend are now together after asking them both several times which they both denied. It’s not even been a week. I’m so heart broken, this girl was meant to be my best friend we was friends for over 14 years. I sat and cried to her and told her how much loved him meanwhile she’s texting him. Telling me she didn’t want to hurt me.