How can I know that their marriage won’t last?

I’m going to include the link to my OP. My ex cheated on me for months with someone, left me, apparently not for him but for someone else, now they’re married and it’s only been a year since she left me for him. She told me she wanted to marry me & loved me so much right before discarding me, that I was the greatest guy she ever met, and she couldn’t wait for our future. She then threatened to call the police when I begged to talk, and blocked me, then her friends/boyfriend called me a stalker when I stupidly made a fake number or two to beg to talk and understand what happened that she switched so quickly. I know this was crazy ex behavior and I regret it deeply. She told me I’m a narcissistic stalker and need mental help and she prays for me. She justified her cheating that she thought I’d want to die if she left me, because I struggled with anxiety whenever she’d cheat and randomly break up with me. She told me she’d never cheat again on anyone and told me I’ll never be a victim in our story. She’s smeared me publicly and is now happy & married. It feels like she’ll never cheat on him because she fears abandonment and is actually in love with this guy. Plus it’s public and everyone knows about him unlike me. Her wedding looked amazing. Everyone commented how they’re happy she found love after “surviving toxic relationships” and they’re so proud of her. Everyone looks so happy in the photos. They’re both madly in love and talking about having kids from what I heard. She’s not the type to ever want to divorce. I don’t think she’ll do him dirty. https://www.reddit.com/r/BPDlovedones/s/AtmMXrpWmM