Best friend is making out with my ex

So people will tell me not to be pissed cause it’s my ex but once again I am so my ex was a shit person and I’m not saying it out of jealousy because he was manipulative and made me feel like shit . I have told my best friend who he really is and once again she ignores my feelings and is currently out sucking his face off it’s not really about my ex more my best friend I feel betrayed and hurt and idk what to do some help would be greatly appreciated even just advice or shared experiences xxx