Bad friends

So I am wanting to discontinue a friendship and I really don’t want to have that conversation with her because she never admits or realizes when she is in the wrong, and I don’t know if I should just bare through the conversation or just ghost her until she hits me up? She has been one of my really good friends for like 4 years..we’ve been on and off because whenever she had a boyfriend she wouldn’t hit me up until they would break up most of the time. She has also been really good friends with my ex for even longer. She hooked me and my ex up ( we r working on getting back together) and we all three would always hangout. Me and my ex have been broken up for a year and she just started hanging with him again. She has also recently started being friends with this girl in our town who we all know and she invited him to my Ex’s party when I was out of town. Her friend and my ex have known eachother all throughout highschool and had the same friends and nothing ever happened romantically between them and they’ve never flirted before. But at the party all of a sudden she started telling my friend how cute he was and all this stuff. My friend kept telling my ex what she was saying and told him to go kiss her and stuff but he thought that was weird. The next night the chick was having people over and my friend begged my ex to come and the entire time was trying to get them to hook up cause her friend wanted to...and they did. I just feel so betrayed by her.. I’ve had her back so many times and been on her side when no one else was. She knew that this situation would hurt me so much, yet she encouraged it . If she had my best interest at heart she would have shot the idea down and not feed into it. Even though he can make decisions himself I do believe if she wasn’t involved, being the matchmaker, it wouldn’t have happened cause I know the chick isn’t like that and neither is my ex! She’s let me down so many time and this is the last straw I don’t need her as a friend if she’s not gonna have my back like I’ve had hers.