Coping w/ kids father girlfriend

How do you cope with knowing someone couldn’t give you the bare minimum but is willing to do it for another? I know I am broken, I know I need to find myself and love myself. But like what the hell, why is it that everything I asked for he’s giving it to her?

Edit: I just want to add I’m am working on letting him go. Now the girlfriend is MAD DISRESPECTFUL and has talked trashed about our daughters. She even threat to harm them if she would ever see them. this is why I’m not understanding why he’s holding his ground and letting her disrespect OUR daughters. Why would you want to be with someone like that?