I need to know if I’m crazy...

I am a single mother to a beautiful daughter. But I literally feel like I’m going crazy and I just need help. My ex (baby daddy) hasn’t helped me once since I left him when she was 6 months old. It’s three years on and still nothing. Last year he started dating his ex (also a baby mother of his first son- his second son was from another woman -they are three months apart). He recently started dating her last year after 2 years of according to
Him “waiting for me to stop being angry”. Which is a lie because he was hoeing around anyway. Anyway. So I found out they were dating and turns out they have twins ( 6 months after my daughter was born 😳😳😳)- which means she was pregnant when I was still with him. I didn’t know. I literally found out two years after they were born. He told absolutely no one. Only his family knew. While I was dating him this same woman terrorized me , she shared photos of me on social media and stalked me constantly, she even still referred to herself as his wife. (She used witchcraft (big thing in sa) against me and even though I didn’t believe in it... some weird stuff happened to me and my child). But they back together.... am I crazy to think that that’s ansolutely ridiculous? Like what is going on? Am I worthless to him? Is there something wrong with me that he would choose her over me? I’m not saying I’m perfect but I know that I’m not crazy, I haven’t behaved in any manner that would be disappointing, I am a committed mother to my daughter, I fully support her ... not to mention up to six months ago I was even assisting him in paying his legal bills. This same woman has upped and left her kids behind and moved to the city he lives in to
Live with him- is this a mother? I don’t know what my question is really? Am I wrong to feel that he may be with her for convience? I feel like I have been unfairly treated- even though I know it’s a part of life, but am I wrong to feel that I am better than she is...maybe I’m not better for him though- maybe he wants someone whose desperate enough to be with him? Help me? I feel so worthless and ashamed of myself. He hardly sees his daughter, let alone support her. He sees her for five minutes and than spends the rest of his eeekend with her and their kids. Why? Why was I the one that got thrown away when I feel I brought more to the table